Yaoi is another term for a certain type of slash in anime or manga continua. The term purportedly originated as an acronym of the phrase "yama nashi, ochi nashi, imi nashi," which means "no climax, no point, no meaning."[source, please!] More specifically, it refers to male/male slash, while yuri refers to female/female slash.
Note that despite the anime/manga origin, this term is rarely actually used in Japan nowadays; the genre is referred to as BL/boys' love in the country. Slash shipping in fandom (slashfics, slash fan comics) is called fu/fumuke 腐/腐向け (rotten/for the rotten).