Here's a brief introduction to GIS by Pima County's John Regan. John describes GIS from a government and public works viewpoint.
See ESRI's What is GIS?.
What is a GIS? Provided by Montana Natural Resources Information System, NRIS
The U.S. Geological Survey's What is a GIS?
We've saved this old slide show from 1998 because we believe it's still relevant.
Making GIS Happen: A Manager's Guide to Successful Geographic Information System by Tom Palizzi, ESRI Denver.
GIS is part of the larger field of Geomatics. See the Complete Coverage Guide to Geomatics provided by Leland-West.
