1. The Unixsuperuser account (with user name "root" and user ID 0) that overrides file permissions. The term avatar is also used. By extension, the privileged system-maintenance login on any {operating system}. See root mode, Go root, wheel. [JarGon File] (1994-10-27) 2. root directory. (1996-11-21) 3. root node. (1998-11-14)