A person using software on a daily basis.  Adding an appointment to a PalmPilot, telling the ATM that they want money from their Savings Account, using prepaid telephone calling cards.

It's the EndUser for whom the UserInterface is designed.    

Given a set of keys and a description of where it is, almost anyone I work with could find my car, start it up, and drive it home -- without a UserManual. (Except of course my four year old nephew, he gets car sick).