The word yaoi stands for yama nashi ochi nashi imi nashi, which means "no climax, no punch-line, no meaning." The reason it stands for this is that, in Japanese, yaoi is BL without plot, skipping any romantic development and focusing only on the sexual parts. When yaoi is used as a general term for gay scenarios in English, it includes bara artwork made by and for gay audiences. Meanwhile, bara will have hairier, more muscular, fatter male characters. In practice, yaoi has "hot guys," ikemen イケメン, and "beautiful boys," bishounen 美少年, that girls find attractive, slender, no facial or body hair, fashionable, so they're basically drawn as the love interest of a shoujo 少女 manga, a prince in search of his princess, except the princess is a dude in this case. The difference between yaoi and bara is that yaoi, like BL, targets a female audience, while bara targets a gay, male audience. Baraīoth yaoi and bara 薔薇 are genres of gay fiction. In English, although the numbers are very small in comparison, more people search for yaoi manga than BL manga, which the opposite of what happens in Japan. Searches for yaoi やおい are practically nonexistent compared to BL in Japanese.
In English, yaoi is the most common term for explicit gay fiction. The term yaoi refers mainly to explicit gay fiction, but the way it's used in English and in Japanese differs. Left: Usui Kenta 雨水健太 Right: Maaka Ren 真紅煉 Anime: Karin かりん (Episode 12, Censored)