GIS stands for Geographic Information Systems. This includes the various technology, data, people, methods and resources required to operate the system. Most government work is location based. GIS is used to support business functions by:

Modeling what if scenarios
Identifying patterns or concentrations of occurrences
Presenting trends to examine change over time
Finding locations based on addresses, latitude/longitude info, zip codes, intersections, etc.
Answering "where" questions related to specific conditions or criteria 
Providing routing for field work
Tracking and scheduling maintenance projects
Displaying and exporting map images
Synthesizing information for ease of understanding and data driven decision-making