Squashfs is a compressed read-only filesystem for Linux. Squashfs is
intended for general read-only filesystem use, for archival use (i.e.
in cases where a .tar.gz file may be used), and in constrained block
device/memory systems (e.g. embedded systems) where low overhead is
needed. The filesystem is currently stable, and has been tested on
PowerPC, i586, Sparc and ARM architectures.

squashfs-tools are the set of tools to manipulate squashfs images.