Shapefiles are a simple, non-topological format for storing the geometric location and attribute information of geographic features. The shapefile format defines the geometry and attributes of geographically-referenced features in as many with specific file extensions that must be stored in the same project workspace.
A shapefile is really a directory of a number of files. Three files are required to define a shape, but there may be many more, depending on how much data is associated with the geographic objects.
They are:
.shp - the file that stores the feature geometry. Required.
.shx - the file that stores the index of the feature geometry. Required.
.dbf - the dBASE file that stores the attribute information of features. Required.
.sbn and .sbx - the files that store the spatial index of the features. Optional.
.fbn and .fbx - the files that store the spatial index of the features for shapefiles that are read-only. Optional.
.ain and .aih - the files that store the attribute index of the active fields in a table or a theme's attribute table. Optional.
.prj - the file that stores the coordinate system information. Optional.
This file can be created with and is used by the ArcView Projection Utility.
It is not used by ArcView GIS Version 3.x or older versions, or by ARC/INFO
versions previous to version 8.0.
.xml - metadata for ArcInfo 8.0, for using shapefiles on the Internet. Optional.
Note that this information can also be obtained through ArcView Help.