Unix is a computer operating system designed to enable computers of various types to run applications and share resources.
Years of development, thousands of lines of code, and millions of man-hours have been spent on creating a piece of software; which, in the final analysis, spends much of its time displaying a text-based user interface which a blind wombat could have designed with more flair.
Unix was designed primarily to make it easy for clever people to do many clever things. As a result, it is also easy for stupid people (most of us) to do a vast amount of stupid things ... and sysadmining a Unix network is like babysitting 50 weasels in a sweet shop.
Unix was originally designed by AT&T in 1969, and subsequently developed into numerous variations, such as 'Linux' (created by Linus Torvalds). Linux was released at no charge as an alternative to the overpriced operating systems available commercially.