"Bishonen" literally means "beautiful" (bi) + "boy" (shonen). A pretty girl is thus known as a bishojo (where "shojo" means girl). The term applies to young males (approx. 12 - 17 years old) who are very attractive, pretty, and even feminine to some degree (i.e. they have long hair, slender builds, might be gay, etc.) I kinda expanded the term to include any handsome anime male regardless of age, which is kinda confusing, but "bishonen" was the easiest way I could think of to group all the pretty guys I like together. Yes, technically, this site is full of bishonen and "biseinen" (beautiful men), as I have a self-imposed age criteria, but way back when, I didn't know there was a difference.