The GI stands for Geographic Information. The S can be either Science or System. You will often see them used interchangeably because they are very closely related. Basically, you do GIScience with a GISystem.
The science and study of geospatial information:
GIScience is a framework we use to understand spatial information.
Any system or tool we use to store and analyze geospatial information can broadly be considered a GISystem.
GIS can be used to help solve a wide range of geographic problems in different fields:
GIS is an acronym that stands for: