Aniblogger (n.)
A blogger who focuses on anime. See ‘Blogger (n.)’.

Anime (n.) ah’-nee-meh
Strictly speaking, in Japan anime merely refers to anything animated. However, anime in the West is mostly simply understood as animation produced in Japan, though the definition has expanded in recent years to include that from other countries which is influenced by Japanese animators.  Described as being “characterized by colorful graphics, vibrant characters and fantastic themes,” the form differs markedly from traditional Western animation through it’s visual and directorial style and by commonly employing mature themes and fantastical stories.  Well-known examples of anime include Pokemon, Naruto, and Spirited Away.

Bishoujo (n.)
In Japanese, it literally means “pretty girl”. This usually translates to young, attractive, anime-style females within Japanese media. This is often referred to in bishoujo-style figures or bishoujo games within the visual novel, galge genre. See ‘Figure (n.)’ and ‘Galge (n.)’.

Bishounen (n.)
In Japanese, it literally means “pretty boy”. Most often this refers to male characters with extremely feminine, but still attractive, appearances. 

Blog (n.)
A website dedicated to posting personal opinions or articles on either various topics, or one particular topic. Sometimes this also includes various links to other blogs or web pages.

Blog (v.)
To write a blog. See ‘Blog (n.)’.

Blogger (n.)
One who blogs. See ‘Blog (v.)’.

Blogosphere (n.)
The complete collection of online bloggers, and the community created among them. See ‘Blogger (n.)’.

Canon (adj.)
Although used to refer to religious texts, in the context of the otaku community, used to refer to story or events intended by the original writer or creator.

Chibi (adj.)
Derived from Japanese, meaning small, though in the context of anime and manga it usually refers to an artistic representation of a character with an enlarged head and otherwise small proportions, giving it a “cute” appearance.

Cosplay (n.)
Coined by the Japanese by combining the terms ‘costume’ and ‘play’. Cosplay primarily involves dressing in costumes based on characters from various media, primarily movies, comics, television series, video games, and others.

Cosplay (v.)
To engage in cosplay. See ‘Cosplay (n.)’.

Cosplayer (n.)
One who engages in cosplay. See ‘Cosplay (n.)’.

Crunchyroll (n.)
A popular Western video streaming site that obtains licenses for current and previous anime and Asian dramas and makes them available for free with ads, or by premium subscription. Check it out here.

Dating Sim (n.)
Dating Simulator. A sub-genre of visual novels that focuses on building a romantic relationship with one of several available characters. This can either be completely story-based on built off of various choices made throughout the narrative, or based on a point system depending on actions taken with the character (or a combination of both). An example of the former is a visual novel like Clannad, while an example of the latter is the DS game Love Plus. See ‘Eroge (n.)’, ‘Galge (n.)’, ‘Visual Novel (n.)’.

Dub (n.)
Often the abbreviated term for the English dub, or English voice-over, of a piece of media. Though most associated with anime, live action films can also have dubs, as well as any other voiced media, such as visual novels. The “Sub vs. Dub” argument is one of constant debate among the Western otaku community, questioning whether consuming media in the original language is superior to consuming it in translated and localized form. See ‘Anime (n.)’, ‘Otaku (n.)’, ‘Sub (n.)’, ‘Visual Novel (n.)’.

Ecchi (adj.) et’-chee
The Japanese term for lewd, though the context of the term can extend to many things sexual in nature. The term if often used in anime.

Ecchi (n.) et’-chee
Ecchi is often used as a blanket genre for anime or manga focusing on sexual situations. Usually less severe than ‘hentai’. See ‘Hentai (n.)’.

ED (n.)
Stands for ending. Refers to the ending song and/or visual that accompanies any media that can accommodate one, including but not limited to anime and visual novels. See ‘Anime (n.)’, ‘OP (n.)’, ‘Visual Novel (n.)’.

Eroge (n.) eh’-ro-geh
A game, usually a visual novel, which contains erotic content. See ‘Visual Novel (n.)’.

Fan Art (n.)
Art created by fans that generally feature a character or set of characters created by a different established artist. One popular avenue for shipping characters not normally “canon”. Popular especially with the online otaku community, particularly on sites such as Deviantart and Pixiv. See ‘Canon (adj.)’, ‘Otaku (n.)’, ‘Ship (v.)’.

Fan Fiction (n.)
Stories written by fans that generally feature a character or set of characters created by a different established artist. One popular avenue for shipping characters not normally “canon”. Popular especially with the online otaku community. See ‘Canon (adj.)’, ‘Otaku (n.)’, ‘Ship (v.)’.

Fanboy (n.)
A male who shows an abnormally large amount of appreciation for a product or creator of a product, such as a particular anime or anime studio.

Fandom (n.)
The population of fans of a particular product, creator of a product, or particular genre of products. A term often used to refer to active Internet users who frequent fan-related websites.

Fangirl (n.)
The female equivalent of a fanboy. See ‘Fanboy (n.)’.

Fanservice (n.)
Aspects of a visual medium used as “sex appeal”, often but not always lewd in nature. A relatively tame example is exposing swimsuits being focused on in a particular episode, while a more extreme example is the inclusion of explicit sexual content, usually referred to as ecchi or hentai. Fanservice can be geared toward both males and females, though it is more often associated with being aimed at a male audience. Two of the most well-known examples are the infamous anime beach and hot spring episodes. See ‘Ecchi (adj.)’, ‘Hentai (adj.)’.

Figma (n.)
A popular line of figures distributed by Good Smile Company that are relatively small in size and focus on being highly pose-able. See ‘Figure (n.)’.

Figure (n.)
Also known as ‘Figurine’. A figure is a (usually) small-scale statue of a person or creature. The word figure often refers to something that is not pose-able (while terms like Figma or action figure are often used to refer to pose-able ones), though that distinction is not exact. Figures are often associated with anime and video games. See ‘Anime (n.)’, ‘Figma (n.)’.

Forum (n.)
Usually used in reference to an Internet forum, a forum is an online discussion board where many users can interact by creating and replying to various threads, organized by type. Many forums are themed on a particular type of media or particular product, allowing fans of similar products to interact.

Galge (n.) gahl’-geh
Coined by the Japanese adoption of gal’ (girl) game. Galge is a genre of visual novel and dating sim that focuses on developing a romantic relationship with a girl among a cast of several attractive, anime-style girls. Although eroge is technically a sub-genre of galge, the term galge is often used to refer to non-explicit dating sims. See ‘Dating Sim (n.)’, ‘Eroge (n.)’, ‘Visual Novel (n.)’.

Gender Bender (n.)
Although gender bender has several definitions, the definition most often used in the otaku community refers to a genre of one of three primary possibilities: (1) one or more characters literally changes biological sex due to either fantastical or scientific means, (2) one or more characters dress and/or act in the manner of the opposite sex to some extreme degree, and (3) a piece of fan fiction in which character sexes are swapped in order to change character, as opposed to being a plot point.

Harem (n.)
A popular genre of anime and manga that generally features a main male character with several female side characters that are simultaneously romantically interested in him. This often takes form as a romantic comedy. See ‘Anime (n)’, ‘Manga (n.)’, ‘Romcom (n.)’.

Hentai (adj.) hen’-tie
Hentai, by itself, literally means weird or perverse, but it usually a shortened term for “hentai seiyoku”, which narrows it to mean of a sexual nature.

Hentai (n.) hen’-tie
Hentai is often used as a blanket genre for anime or manga related to pornography. Usually more severe than ‘ecchi’. See ‘Ecchi (n.)’.

H-Game (n.)
An eroge that contains sexually explicit content. See ‘Eroge (n.)’ and ‘Hentai (n.)’.

Hikikkomori (n.) hee-keek-ko-mo’-ree
A phenomenon not exclusive to, but dominated by the Japanese population. A hikikkomori is known as a recluse, staying primarily in his or her room all day, every day, normally surfing the web, watching anime, playing games, or participating primarily in other activities generally associated with otaku. This is often due to a lack of openings in the Japanese job market and a comfortable reliance upon parental or guardian-provided living quarters and allowances.

Honorifics (n.)
Japanese suffixes attached to names equivalent to English titles like Mr., Mrs., and Dr.. Examples include ‘san’, ‘kun’, and ‘chan’. For a more full explanation, check here.

Imouto (n.) ee-moe’-toe
The Japanese word for little sister.

Josei(n.) jo’-say
A term for manga which are published in a magazine with a target audience of adult females. See ‘Anime (n.)’, ‘Manga (n.)’.

Kinetic Novel (n.)
A visual novel which contains no choices. See ‘Visual Novel (n.)’.

Light Novel (n.)
Light novels are another published medium like Japanese manga. Unlike manga, though, light novels are more comparable to the Western book genre of “young adult novels.” Originally, light novels referred to novels, or novellas, written primarily for the teenage audience and released in volumes of somewhere in area of 150 pages. However, the term is now used to refer to any novel that features anime-styled cover art. While they are written much like Western young adult novels, they are often more dialogue-heavy and also include occasional pictures. Well-known examples of light novels include Sword Art Online, Toradora, and the Haruhi Suzumiya series.

Lolicon (n.)
One who is attracted to young, or young in appearance, girls, usually animated. Often associated with pedophilia. See ‘Lolita (n.)’.

Lolita (adj.)
A type of (originally) Japanese fashion that focuses on Victorian-era clothing. Often this is defined little exposed skin, frilly designs, and wide skirts. Often associated with cosplay. See ‘Cosplay (n.)’.

Lolita (n.)
A term coined due to the 1958 novel Lolita by Vladimir Nabokov. In anime and connected forms of media, it usually refers to a woman who appears to be much younger than she really is (often appear pre-pubescent). Sometimes, based on context, the character may be sexually promiscuous.

Maid Cafè (n.)
A cafe that usually serves food and/or drink via waitresses dressed (cosplaying) as French maids. A popular type of establishment in Japan, usually attended by otaku. See ‘Cosplay (n.)’.

Manga (n.) mahn’-gah
Manga (pronounced mahn’-gah) is simply the Japanese form of comics. While comics in the Western world do not hold the vast popularity that manga holds in Japan, the format is similar, playing out in drawn tiles with speech bubbles that convey story and action. Unlike Western comics, however, Japanese manga covers many more genres and holds much more relative interest in its homeland, serving as one of the primary source materials for the higher budget anime medium. They are also read right to left. Well-known examples of manga include Bleach, Fairy Tail, and Attack on Titan.

Mangaka (n.) mahn’-gah-kah
A manga artist. See ‘Manga (n.)’.

Mecha (n.)
A popular genre of anime and manga centered primarily around the use of manned, bipedal robots. Mecha often have teenage main characters and often fall into the genre of shounen. See ‘Anime (n.)’, ‘Manga (n.)’, ‘Shounen (n.)’.

Moe (adj.)
Description for a female animated character that shows qualities counted to be “cute” by viewers. It is often associated with characters who are easily frightened or exhibit “ditsy” qualities.

Moe (n.)
A genre of anime/manga containing numerous “moe” characters. See ‘Anime (n.)’, ‘Manga (n.)’, ‘Moe (adj.)’.

NEET (n.)
Not in Education, Employment, or Training. See ‘Hikikkomori (n.)’.

Nendoroid (n.)
A line of plastic figures created by Good Smile Company based on “chibi” interpretations of popular characters. Nenderoids usually also include multiple face pieces that can be interchanged for different expressions. See ‘Chibi (adj.)’, ‘Figure (n.)’.

NSFW (adj.)
Not Safe for Work. If a picture or video is labelled NSFW, it likely contains lewd or otherwise inappropriate content.

OAV (n.)
See ‘OVA (n.)’.

Onee-chan (n.) oh-neh’-chahn
A familiar, endearing term for big sister. 

Onii-chan (n.) oh-nee’-chahn
A familiar, endearing term for big brother. 

OP (n.)
Stands for opening. Refers to the opening song and/or visual that accompanies any media that can accommodate one, including but not limited to anime and visual novels. See ‘Anime (n.)’, ‘ED (n.)’, ‘Visual Novel (n.)’.

Otaku (n.) oh’-tah-koo
In Japanese, “otaku” (or オタク) means “geek, nerd, or enthusiast” (JED, Japanese-English Dictionary). In Japan, this could include anyone from someone obsessed with reading books, to ancient shogunates, to anime, and anything in between. It truly means nothing more than “nerd”. However, Western culture has adopted the word “otaku” to mean, specifically, anime otaku. While these exist in Japan (and likely comprise the majority of the population accused of being otaku), it is mostly in the English adoption of the word that otaku has come to mean someone obsessed with Japanese media, particularly anime.

Otaku-dom (n.)
Being an otaku.

Otome (n.) oh’-toe-meh
The equivalent of a “galge” aimed for girls, with a mainly male cast of potential romantic partners. See ‘Galge (n.)’.

Otouto (n.) oh-toe’-toe
The Japanese word for little brother.

OTP (n.)
Stands for “One True Pairing”. A term particularly used by a product’s fandom to refer to the preferred romantic pairing. See ‘Fandom (n.)’, ‘Ship (v.)’.

OVA (n.)
A relatively ambiguous acronym standing for English words but originating in Japan which generally stands for “Original Video Animation”. It can also be seen as OAV, or “Original Animated Video”. These are either episodes or short films not released for theaters or television.

R-18 (adj.)
Stands for R-18. A rating usually applied to hentai and eroge products. See ‘Hentai (n.)’, ‘Eroge (n.)’.

Reverse Harem (n.)
A harem, except with a female lead character and male side characters. See ‘Harem (n.)’.

Romcom (n.)
Short for “Romantic Comedy”.

Ship (v.)
To pair a romantic couple of characters not counted as “canon” (intended by the original author) in an existing series. See ‘Canon (adj.)’.

Seinen (n.) say’-nen
A term for manga/anime which are published in a magazine with a target audience of adult males. See ‘Anime (n.)’, ‘Manga (n.)’.

Senpai (n.) sen’-pī
A Japanese term that refers to one who is your senior, usually in the context of someone being in a higher academic year, though not limited to that. It can also be used as a suffix honorific. See ‘Honorifics (n.)’.

Shoujo (n.) sho’-jo
A term for manga/anime which are published in a magazine with a target audience of teenage females. See ‘Anime (n.)’, ‘Manga (n.)’.

Shoujo-Ai (n.) sho’-jo-ī
Literally “Girls’ love”. A genre of anime and manga that usually features several girls who express great interest in each other that can be interpreted as deep friendship, but is generally interpreted by fans as romantic interest. More mild than yuri. See ‘Yuri (n.)’.

Shounen (n.) sho’-nen
A term for manga/anime which are published in a magazine with a target audience of teenage males. See ‘Anime (n.)’, ‘Manga (n.)’.

Shounen-Ai (n.) sho’-nen-ī
The male equivalent of Shoujo-Ai. See ‘Shoujo-Ai (n.)’.

Sub (n.)
Short for subtitles. Refers to translated subtitles usually in the context of translated anime. As opposed to a complete voice-over or dub, a “sub” maintains the original verbal language. See ‘Dub (n.)’.

Tsundere (adj.) tsun’-deh-reh
Originally a term referring to a character that originally displays a cold or heartless attitude toward another, or several other, character(s), but eventually shows a slow change in attitude toward being more affectionate. Now, more commonly refers to a character that displays would-be affectionate behavior by acting cold.

Trope (n.)
Though not its real definition, usually refers to a plot element or trait commonly used in media. An example of a trope is the tragic heroine, or running to school late with a piece of taste in one’s mouth due to being late for school.

Visual Novel (n.)
Visual novels are one of the most unique mediums of Japanese entertainment, and the hardest to compare to Western media. Visual novels are often considered within the genre of video games, which is a bit of a misnomer because many of them are “read” more so than “played”. The closest equivalent to Western media is the choose-your-own-adventure book (no longer of much popularity), though they actually play out more like a mixture of an audio drama mixed with a manga. Although there are differences within the visual novel medium, most are “read” by clicking through dialogue and thoughts of the main character from the first-person perspective, accompanied by background visuals, character sprites, music, and sometimes basic animations, voice acting, or mini-games. Although the visual novel medium is viewed overwhelmingly in Japan as a carrier of the infamous R-18 eroge genre (pornographic dating simulators), there are many visual novels that are clean and well-written. Well-known examples of visual novels include Clannad and Narcissu.

Yandere (adj., n.) yahn’-deh-reh
Originating from the term tsundere, refers to a character that expresses romantic interest through, usually, violent or psychotic or otherwise extreme means, such as kidnapping. See ‘Tsundere (n.)’.

Yaoi (adj., n.) yah’-oh-ee
A genre of anime and manga that focuses on homosexual male characters. Often contains sexually explicit content. See ‘Hentai (n.)’, ‘Shounen-Ai (n.)’.

Yuri (adj., n.) yu’-ree
A genre of anime and manga that focuses on homosexual female characters. Often contains sexually explicit content. See ‘Hentai (n.)’, ‘Shoujo-Ai (n.)’.

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Notes:

Thanks to Annalyn for providing the basic list and structure in her own “Otaku Glossary” found here.