(POSIX) A set of IEEE standards designed to provide applicationpORtability between Unix variants. IEEE 1003.1 defines a Unix-like operating system interface, IEEE 1003.2 defines the shell and utilities and IEEE 1003.4 defines real-time extensions. ["MORe UNIX FOR Dummies", ISBN: 1-56884-361-5] says it stands fOR "PORtable Operating System Interface with an X thrown in to make it sound cooler." (1997-12-04)