POSIX - Portable Operating Standards Interface
Although originated to refer to the original IEEE Std 1003.1-1988, the name POSIX more correctly refers to a family of related standards: IEEE Std 1003.n (where n is a number) and the parts of ISO/IEC 9945. The term POSIX was originally used as a synonym for IEEE Std 1003.1-1988. A preferred term for that standard, POSIX.1, emerged. This maintained the advantages of readability of the symbol ``POSIX'' without being ambiguous with the POSIX family of standards.

TENEX style completion - is a type of command line editing where the words being typed are matched and then completed (if a match is found) by the shell

GNU Project - (GNU's Not Unix) - is a project sponsored by the the "Free Software Foundation". Great site, lots available to you. Check them out. GNU Project