Melee is collectively defined as any action that takes place at the closest-possible range. The term melee in English is officially defined as chaotic, close-quarters combat, however in games it has come to describe absolutely anything that happens at close-quarters, regardless of any violent content or lack thereof.
Vagrants, Mercenaries, Knights, Blades and Billposters all engage primarily in melee combat, and have many skills that only work at melee range.