GIS is an abbreviation for Geographic Information Systems or Geographic Information Science. The textbook definition would go something like this...
GIS - a system of hardware and software for the storage, retrieval, mapping, and analysis of geographic data.
Although that was short, it was confusing unless you knew what it meant to begin with.
Here's a better explanation...
We use massive amounts of computer storage to house a wide variety of data that contains real-world location information. Because of this location information we can overlay different sets of data (e.g. addresses in a police district or parcels in a voting precinct) to derive information from them or to simply reflect their actual relationships. By doing this we can calculate distances, proximities, acreage, patterns, flood levels and a whole bunch of other stuff.
For most people the end result of our services is the creation of a map or the purchase of data. If that is what you need, then go to our GIS Products page to find the necessary order forms.