GIS stands for Geographic Information Systems and is used to integrate, store, edit, analyze, share and display geographic information. GIS works by layering different types of geographic data like raster images and vector data, and uses coordinate systems to project maps onto a two-dimensional plane. Major GIS software providers include ESRI, MapInfo, and Autodesk, while open source tools include GeoServer and PostGIS for storing spatial data in databases. GIS has applications in areas like urban planning, utilities, defense and criminology to help analyze data based on location.