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.
On the other side of the spectrum, you have live mirrors, which keep an eye on the original site and ensure that the mirror remains updated according to the changes on the source.
Download sites for software are often hosted in mirrors. This is meant to facilitate downloads for users by preventing server overloads and offering the downloaders a server close to them, thus being faster.
Consider, for instance, Ubuntu. Canonica, its parent company, is in South Africa. But users are everywhere, especially in Europe and North America, so it makes sense for the company to have mirror hosts in those regions instead of having everybody downloading from South African servers.
