From Kass & Finin (1991):
"A user model is a knowledge
source in a system that contains explicit assumptions on all aspects
of the user that may be relevant to the behavior of the system."
User models (UM) encapsulate:
User profile
User task structures
User preferences
Many of the goal of UMs in common with general HCI:
Better support for user goals, plans and tasks
Clearer and more efficient interaction
Interfaces designed for a wide audience
All user interfaces have some kind of 'model user'
- even if it's just the programmer!