A shapefile is a format used by almost all GIS programs. It provides a convenient interchangeable format if you are moving data from one program or company to another. It consists of at least 3 parts that exist as files with the same priamry name but a different extension:

• .shp - shape format;l contains the feature geometry- lines, points or polygons
• .shx- shape index format- a positional index
• .dbf- an old school file format that is a remnant of the DBase system which is an old database system. This file holds your attribute data such as names, addresses and descriptions

There are a number of other files that may exist depending on the nature of your shapefile:

• .prj- a projection format will be present if you have defined this for the shapefile- important to create for data you will reuse and export often
• .sbn and .sbx- spatial indexes (don't fuss over these but don't delete em anyway)
• .shp.xml- metadata in XML format. Metadata IS important with spatial data, use it!