A classic vector data format in ESRI software (ArcView, ArcGIS …) before geodatabases, as a set of separate files with the same name but a different extension. Whether points, lines, or polygons, geometric objects stored in the file with the .shp extension must always be associated with at least one .dbf file and one .shx file. The .dbf file contains the attribute data in DBF format about the objects contained in a file, while the .shx file stores the index of the geometry. Many other files can be added. The file extension .prj carries information on the system of coordinates and projection. The shape files or form files act in the role of exchange formats in geomatics with Google’s KML/KMZ file format.

http://en.wikipedia.org/wiki/Shapefile