(Verb: Reeming) Slang word for the act of anilingus, or in basic terms, anus licking. The term 'Reeming' is used in particular when the anus in question is unwiped.
Guy 1: Hey, I heard a rumor you and your girlfriend were ass licking each other the other night, literally.
Guy 2: Yeah, was more like reeming than ass licking though, Dude.
Guy 1: Gross. Dude, doesn't she wipe?
Guy 2: She doesn't need to, I cleaned her ass for her.