Definitions for "Mirror Site"
This would be an identical site with a different URL. Many people feel this will help them obtain better rankings, however search engines feel this is a form of spam.
A mirror site is usually set up due to overwhelming traffic on an existing web site. A mirror site is a site that is kept separate from the original site but contains the same information as that site. This is an alternative to users who attempt to go to a web site but cannot due to traffic problems.
duplicate site (same file) to reduce activity on server
an alternative location from which a file can be downloaded
a very common occurrence when downloading something off the Internet
Keywords:  maintains, computer, system
a computer system that maintains