A mirror is something that you can see your reflection in. Most mirrors consist of a sheet of glass with a sheet of metal behind it. When light hits the metal, it reflects onto the glass and produces the image you see. In the computer world, however, a mirror is a Web or FTP server that has the same files on it as another server. Its purpose is to provide an alternate way to access files when the main server is so swamped with people connecting and downloading files that other people can't get through. Unlike real-life mirrors, when you download a picture off a mirror server, the image isn't backwards.