[ESRI software]
Usually a text file named prj.adf that is associated with a coverage, GRID, or TIN. The PRJ file contains the coordinate system information for the data. In a more general sense, PRJ can refer to the coordinate system of data even if the information is not stored in a prj.adf file. For example, "The PRJ of the shapefile is WGS 1984 UTM zone 15 north."