@Bi Aunty you never asked
Heya! BL, at least from what I've seen, is a genre with yaoi being a subgenre within BL. Though the terms are used differently, BL usually being used when describing a story with minimal or no sm** while yaoi has sm**. It's the same with the GL genre and yuri sub-genre, if I'm not mistaken! But please don't take my word for it, the difference differs from person to person.
*does finger guns of greeting*