A .pkg file is essentially an archive or installer package used by Sony PlayStation systems. On a standard, unmodified PS3, the system uses these files to install official game patches, DLC (Downloadable Content), system firmware updates, and PlayStation Network games.
PKG games often load slightly faster because they are installed directly to the internal hard drive, avoiding the "stutters" sometimes seen when a console reads from both a virtual disc and installed data. ps3 pkg download
: