What is GIS?

The U.S. Geological Survey (USGS) uses a simple definition for GIS:

A Geographic Information System (GIS) is a computer system capable of capturing, storing, analyzing, and displaying geographically referenced information; that is, data identified according to location. Practitioners also define a GIS as including the procedures, operating personnel, and spatial data that go into the system.

Related Sites:
USGS – What is GIS?
GIS.com – Geographic Information System
GIS Software
Geographical Information Systems (GIS) WWW Resource List