Unix

Unix is an Operating System written by Ken Thompson and Dennis Ritchie at Bell Labs in 1969.

Originally UNICS, which stands for Uniplexed Information and Computing Service, which was a lesser variant of a project called MULTICS, Mulitplexed Information and Computing Service.

Unix is more a class of operating system than a specific operating system. There are two basic variants: BSD and System V. Most Unix and Unix-like operating systems fall neatly (or less so) into one of these categories.