RoyEd is a Yaoi pairing between the main character Edward Elric and sub-main character Roy Mustang in the Anime Fullmetal Alchemist. The general idea behind the pairing is the classic "opposites attract" because as Edward is a wandering character through most of the series and the few times that he confronts Roy, his superior officer, they often get into fights where Ed starts yelling for mostly unknown reasons besides being called short and Roy silently fuming behind his desk before either making an outburst himself or starting to mess with Ed's head. It is one of two most common Yaoi pairings in the series. The other is Edvy, or Ed/Envy pairing.
OMG, I can't stop reading all this RoyEd fanfiction, it's so addicting!