What is GIS?
WikipediA describes Geographic Information Systems (GIS) or geospatial information systems as a set of tools that captures, stores, analyzes, manages, and presents data that are linked to location(s). The answer to this question for a GIS Professional, however, almost always boils down to the distinction between "mapping", which is simple and tangible and something people can easily wrap their heads around, and real analysis. 
In the simplest terms, GIS connects information about where things are located with information about what those things are like; what they look like, how they work, what they do, etc.ESRI says "a geographic information system (GIS) integrates hardware, software, and data for capturing, managing, analyzing, and displaying all forms of geographically referenced information". Everything on the surface of the earth has a spatial location, or a coordinate which references its position on the earth. Once the location of an object has been determined, or collected (with GPS for example), that object is geographically referenced and can be stored, analyzed and displayed in a GIS.
In more technical terms, a GIS is an information system that is designed to work with data referenced by spatial or geographic coordinates. It is both a database system with specific capabilities for spatially-enabled data, as well as a set of operations for working with (analyzing) the data. GIS goes beyond simple cartography ("mapping"), allowing us to identify, view and evaluate relationships between spatial data. This can be something as simple as looking how close a coffee shop is to your office, or something as complicated as determining the potential effect of a wind farm on goose migratory patterns. These more complex analyses demonstrate the power and usefulness of GIS.
In terms of what we do here at the University, GIS is a powerful tool in the management and monitoring of the many structures and systems we maintain above and below ground. Our GIS allows us to store the information about these systems, keep them accurate and up to date, and view them together so that we can observe their location and spatial relationship with one another. We can analyze these spatial relationships, and dispense this information via GIS applications, the web or simple maps. GIS makes map data interactive, and as a result, makes it more powerful.