An UNIX administrative command for making filesystems on new partitions (or in case you want to get rid of the old partition's contents).
In Linux, this is actually a facade for programs to create specific types of filesystems; For example, mke2fs will create ext2 filesystem, and mkfs.minix will create Minix filesystem.
Example (in Linux):
mkfs -t ext2 /dev/sda0
(Will make an ext2 filesystem on the first SCSI hard disk's first partition.)