From Fan History Wiki
Yaoi is actually an acronym for "Yama nashi, Ochi nashi, Imi nashi" which translates to "No climax, no resolution, no meaning." This term is used to describe stories or art that features a male/male relationship. Its counterpart, for female/female, is Yuri.
This section needs more information.
The following term dates to 1970 in anime/manga fandoms:
- Yaoi or YAOI stands for Yama nashi, Ochi nashi, Imi nashi, which means "No climax [of a story - ed. note], no plot, no meaning." The fan fiction genre supposedly stresses sex scenes, lemons with possible portrayal of violence. It led to a more humorous acronym interpretation of the meaning of yaoi as yamete, oshiri ga itai, translated: "Stop, my ass hurts".
- Yaoi is an acronym that stands for "yama nashi, oshi nashi, imi nashi" which means no climax, no point, no meaning. It was originally used to describe a manga or doushinji story which had no plot other than to get two male characters in bed with each other. In the transition to the West, it came to be used for text stories as well. Yaoi in itself is a mainly doushinji innovation for such popular manga as Yu*Yu*Hakusho (YYH) and Gundam Wing (GW), a doushinji being a comic based on a particular manga drawn by fans. For original yaoi manga, the term june is more appropriately used. For Western fans, they may be more familiar with the term "slash" which is similar, but not the same as yaoi. The term yuri means basically the same thing, but refers to female - female stories instead. 
- (Japanese translates: boy love)
- Form of adult fanfiction (also found as shounen-ai)
- Deals man to man relationship. It doesn't necesseraly have sexual content (usually does though) but it hints of a certain form of stronger bonding.
The analogue for girl to girl is shojo-ai. 
- Yaoi: A label found on fanfic, fanart and sometimes even site content—should be considered as a very serious warning. Originally, YAOI stands for yama-nashi (without climax), ochi-nashi (without a conclusion) and imi-nashi (without content) within a manga/anime context. In other words, a PWP that doesn't sure any function beyond getting two/more people into the sack together. It has now come to occupy almost the same meaning as slash. The difference being, according to one article on Aesthetism.com, that yaoi needs less plausible reasons for slash to exist. And so slash is not yaoi (except perhaps when it's a PWP), but with some more plot, yaoi can sometimes be slash.
- YAOI - this means, "Shounen ai". This means a boy x boy relationship. Still don't get it? Imagine a cute guy kissing, hugging, petting.....another guy! There's lots of that in this site...-_- 
- Yaoi Yaoi: Boy/Boy Relationships. Slightly different from shonen-ai (boy love) because this one usually has sex, or more than just a small attraction. A bit heavier stuff. ^_~ 
- Yaoi is an acronym that stands for "yama nashi, ochi nashi, imi nashi," which means "no climax, no point, no meaning." A strict definition would have it mean "sex between men just for the sake of sex," and drawn by an amateur doujinshi managaka (person who writes/draws manga). But it has evolved from that meaning, especially in the west. It's now used as a general term for male/male relationships, but still emphasizes the sex over the emotions. Or at least, if there are emotions, there's sex, too. It's also supposed to be used for non-original material (i.e. putting Lantis and Eagle in bed together, instead of making up one's own characters).
- Some of the fics (make that most) on this page are Yaoi, meaning male/male relationships. 
- YAOI/SHOUNEN AI
A type of fic implying boy to boy relationship. We don't write or read or host this kind too. But some people just do. Anyway, just for information sake, we're going to tell you about it. You can distinguish yaoi/shonen ai warnings from couples because instead of a slash (/) an X is put instead. So it would be GXV (GokuXVegeta) and the like.
- Yaoi: Guys making steamy butt love with each other, usually contains a lemon or at least a lime
- Yaoi: Male/male relationships
- Yaoi - see slash, only more likely to be graphic and have no plot. 
- Yaoi: Anime fanfic term for male/male relationships. Can include sex. 
- yaoi Stands for "yama nashi, ochi nashi, imi nashi" which means "no climax, no point, no meaning." Yaoi involves a male-to-male relationship often synonymous to shounen-ai , but more erotic in nature.
- yaoi is a form of romantic expression, dealing with male/male relationships. Yeah, that's right. Guys bonking each other. 
- Yaoi - a story with graphic male/male sexual content. Contrary to popular belief, yaoi is not a Japanese anagram of "Ow! My ass hurts!". The lesbian equivalent is Yuri. 
- Yaoi: Love between men, particularly of a sexual nature. 
- Artwork, comics, games, movies, stories, etc. involving male x male relationships of a sexual nature. "Yaoi" is an acronym for "yama nashi, ochi nashi, imi nashi (no meaning)" which translates to "no climax, no point, no meaning"... an old joke is that it's an acronym for "yamete kudasai, oshiri ga itai yo" (stop it, my butt hurts). Yaoi can contain shonen-ai elements (and often does) or it can be purely sexual. The realism of the pairing is irrelevant. Note that yaoi should really only be used to refer to pairings taken from Japanese media and is denoted Seme(top) x Uke(bottom)... in the Western culture the proper term would be slash. The female x female equivalent is called "yuri."
- YAOI: In anime, refers to PWP stories about gay relationships, often tragic ones.
- Yaoi = The original definition of yaoi is: An acronym for "yama nashi, ochi nashi, imi nashi": no mountain (ie peak; climax), no point, no meaning. No attempt at plot or meaning or character development. The point is sex, and the relationship outside the yaoi doesn't matter. Drawn/written by fans using other people's charas.
- Nowadays, fanfic writers tend to use the term Yaoi in the broad sense for any m/m stories and fanfics, especially those containing lemons.
- Yaoi comes from the Japanese phrases "yama nashi, ochi nashi, imi nashi" which means "no point, no climax, no meaning." Yaoi is a reference to some dojinshi artists that focus mainly on sex instead of a plot. The term yaoi originally referred only to dojinshi, but has broadened to refer to the male/male fandom in general. Today, the word yaoi is used to refer to homosexual relationships between men in anime and manga. 
- YAOI—A term used to describe slash, anime specific. Yaoi is more "hormonally" run, more sexual, less lovey-dovey, enjoy heavily and written by fangirls. Any fic that uses this code is one to be avoided. Not because of homosexual relationships, but because it's probably poorly written and lacks a well made relationship.
- Yaoi: an anime/manga story in which the plot is centered around a romance relationship between two male characters, usually at least one of them being very effeminate. There is a good amount of yaoi in many actual anime/manga series', but yaoi is mostly seen in the world of anime fan art and fanfics, in which the fans(usually girls) take the male characters of a particular anime/manga series and put them in gay relationships. Yaoi relationships are also refered to as "shonen-ai," meaning "boy's love." 
- Yaoi: Boy x boy, means no plot in Japanese. Basically used for mindless screwing. Not as cute and fluffy as shonen-ai is. 
- Yaoi - Acronym for somethingâ€¦the more graphic form of shounen ai 
On September 14, 2006, New York City's Thunder's Mouth Press published Zowie! It's Yaoi!: Western Girls Write Hot Stories of Boys' Love, a collection of yaoi inspired stories. This was the first text-based yaoi book written by Western women.
Below is a partial list of articles and academic sources to help you continue to learn about this term/community.
- Kelly, William W., ed. Fanning the Flames: Fans and Consumer Culture in Contemporary Japan. New York: University of New York Press, 2004.
- Sabucco, V. (2003). Guided fan fiction : Western 'readings' of Japanese homosexual-themed texts. In C. Berry, F. Martin, & A. Yue (Eds.), Mobile cultures : new media in queer Asia. Durham: new media in queer Asia.