1. A metal device that opens or closes a lock
2. A Set of characters, when entered into a software program, unlocks locked features and removes annoying nag screens and trial limits.
3. to scratch up one's vehicle, using a key to do so.
1: Damn it, where did my keys go
2: Someone have a key for Windows 98?
3: That fucking faggot pissed me off so bad, I'm going to key the shit out of his car later on