Yaoi would be guyxguy and Yuri is girlxgirl. These categories can go anywhere from a single halik to sex so be careful and research a show/manga before you watch/read it in case it has something you might feel uncomfortable seeing. Then there is Shounen-ai (Boys-love literally) which is still guyxguy but there is no sex or harsher activity involved. Only kisses and snuggles are involved here. The same goes for Shoujo-ai (Girls-love). No sexual activity involved except for halik and snuggling. =] Hope that helped!