setuid

A process which can set its effective user to super-user (root). That is, although any user can run the process, the process can then execute operations which require root privileges. One example of a setuid process is the ArcStorm wservice process.

Said of a program that runs with the privileges of its "owner" rather than (as is usually the case) the privileges of whoever is running it. Also describes the bit in the mode word ("permission bits") that controls the feature. This bit must be explicitly set by the owner to enable this feature, and the program must be carefully written not to give away more privileges than it ought to.