Yaoi

The word yaoi is derived from the first syllables of each word in the expression, "yama nashi, ochi nashi, imi nashi," which means "no peak, no point, no meaning," and originally referred to badly drawn self-published fan comics (doujinshi). Later, it came to be used for doujinshi with sexual pairings between two males.

In Japan today, the term yaoi is mainly used to point to the sex scenes of a manga or to doujinshi with male/male content. But in the West, yaoi has become a catchall term to indicate any story that includes a male/male relationship and is linked to Japan, be it commercial manga, anime, games, game-based slash fiction, English-language fan fiction, fan art, etc. Unlike "bara" manga aimed at homosexual men, the idealized homosexual relationships depicted in yaoi are aimed at women.

Boy's Love (BL) is the usual term used by the Japanese publishing industry to categorize commercial works focusing on male/male relationships marketed at women. These now include not only manga but novels, CDs, games, and anime.

(definition based on yaoicon.com)