In computer disk terminology, an extent is a set of contiguous sectors that are part of a file. Ideally, a file would need only one extent, but sometimes it must be fragmented into several extents.

Some filesystems locate the blocks of a file with an extent list, which lists the start block and length of each extent. Other filesystems give a list of each individual block. (Each method has its advantages.)

This was brought to you by the Save Our Archaic Technical Terms Society.