UNIX is a portable, multi-user, operating system developed at Bell Laboratories by Ken Thompson and Dennis Ritchie (the inventor of the C programming language) which emphasizes simplicity of implementation. The name is a pun on the MIT-developed Multics operating system which had a much more complex implementation.
Web servers running on UNIX-based systems accounted for 83% of the total servers according to information gathered on a normal WebCrawler indexing run in the fall of 1995.
If you ever see the word UN*X, it's still our pal UNIX. It was written that way in order to avoid legal problems, as UNIX was a word trademarked by AT&T. Lawyers now say that the trademark indicators after every use of the name have no legal force, but the use of UN*X still occurs. There are those who think that it is written that way out of reverence, just as in certain religions the name of the deity is never spelled out in full.