A reference framework consisting of a set of points, lines, and/or surfaces, and a set of rules, used to define the positions of points in space in either two or three dimensions. The Cartesian coordinate system and the geographic coordinate system used on the earth's surface are common examples of coordinate systems.
In ArcGIS, a reference system that locates a position in space and defines the relationships between positions. Coordinate systems enable individual datasets to be georeferenced to each other. The specification of a coordinate system is one of the initial steps in creating a new feature class or raster dataset. Three coordinate systems commonly used in ArcGIS include geographic, projected, and vertical.