Contains extra CRS defined by ESRI (and other parties) in the EPSG namespace. Those CRS are not defined in the official ESPG database, but are used widely enough to warant an optional plugin in Geotools. This plugin do not contains any definition already found in the official EPSG database - it is not a replacement for epsg-hsql or epsg-postgresql. One of the above plugins (at user choice) should be in the classpath.