1. A geographic information system (GIS) is a system designed to capture, store, manipulate, analyze, manage, and present spatial or geographic data. GIS applications are tools that allow users to create interactive queries (user-created searches), analyze spatial information, edit data in maps, and present the results of all these operations. Since many kinds of data have important geographic aspects, a GIS can have many uses: weather forecasting, sales analysis, or population forecasting.
2. A GIS enables you to envision the geographic aspects of a body of data. Basically, it lets you query or analyze a database and receive the results in the form of some kind of map.
3. QGIS is a free and open source Geographic Information System, with which you can create, edit, visualize, analyse and publish geospatial information. QGIS is licensed under the GNU General Public License. It supports numerous vector, raster, and database formats and functionalities.
4. QGIS (previously known as Quantum GIS) is a cross-platform free and open-source desktop geographic information system (GIS) application that supports viewing, editing, and analysis of geospatial data.
http://searchsqlserver.techtarget.com/definition/GIS (1.); https://en.wikipedia.org/wiki/Geographic_information_system (2.); http://qgis.org/en/site/ (3.); https://en.wikipedia.org/wiki/QGIS (4.)