An operating system developed at AT&T Bell Labs by Ken Thompson and Dennis Ritchie, and further extended at the University of California, Berkeley, by a number of students, including Bill Joy, one of the founders of Sun Computers. The key feature of Unix is that while all versions of Unix are not the same, it is an open architecture and not proprietary to any hardware vendor. This means that application programs are more easily ported between different versions of Unix than between any other proprietary operating systems. See open architecture.
A genre of computer operating system originally designed to run on VAX-type miniframe systems by a group at Bell Labs back in the 1970s. It later branched when people at Berkeley in California wrote new pieces to make it better and faster, and ultimately ended up with their own flavor of the system. Different heritages morphed in different ways, and ultimately propagated to desktop computers by the advent of Linux. Most species of unix are freely available and modifiable, resulting in a plethora of variations and available programs. Although Unix is used for serious projects in the scientific community and runs many business backends plus a lot of the servers running the Internet, it's often seen as a hobbyist's system. Commercial distributions have made setup and use much easier over the years, but it isn't the kind of thing you'd want to have to explain to your mom. Most hardcore computer users use some form of unix and detest Windows and Mac machines.
A multi-user computer operating system developed by Bell Laboratories. It is the preferred operating system for critical applications and for Internet servers.