A mirror site is an exact copy of a website or any collection of files hosted on a server other than the original one.
And why would anybody just produce an exact copy of anything online, we hear you ask?
There are plenty of reasons. For example, software companies create several mirrors of their repositories to ensure access from anywhere globally. Others do it to plagiarize a successful website. Another good reason is to prevent server overload when there is an increased traffic flow. Less commonly, a mirror site can be a backup for the original one.
The types of mirror site
Mirrors come in several flavors. The most common one is the static copy. This type of mirror is a snapshot of the original one that doesn’t update itself. Keeping it up to date requires the mirror’s owner to update it by hand.