What is GIS?
Geographic Information Systems
In the strictest sense, a GIS is a computer system capable of assembling, storing, manipulating, and displaying geographically referenced information (that is data identified according to their locations). Practitioners also regard the total GIS as including operating personnel and the data that go into the system. (Source: US Geological Survey)
(Source: US Geological Survey)
Applications and Use of GIS
The following links help describe how GIS can be used.
Map & Geospatial Data Librarian