PET is the file extension used by one of the Linux-based system distributions called Puppy. Technically, a PET file is a file archive that is also an installation package for Puppy Linux.

The author of the first Puppy Linux distribution was Barry Kauler. It is a small tool with low hardware requirements. PET installation files are approximately 100 - 200 MB in size. Files of this type in earlier versions of the system had the PUP extension.