<jargon> A term used to describe programs, hardware or people that use more than their share of a system's resources, especially those which noticeably degrade interactive response.
The term is usually qualified, e.g. "memory hog", "core hog", "hog the processor", "hog the disk". E.g. "A controller that never gives up the I/O bus gets killed after the bus-hog timer expires."
User also hog resources, particularly disk, where it seems that 10% of the people use 90% of the disk, no matter how big the disk is or how many people use it. Once a disk hog fills up one file system, he typically finds a new one to consume, claiming to the sysadmin that they have an important new project to complete.