Cache

In computer terms, a cache is a duplicate of an original data when this original data is time-expensive to fetch.

When this happens, the cache data may be consulted instead of the original data when possible.

This methology is used in many places: processors, disks, web, proxies, etc.

The goal is to reduce the time spent in fetching the data so, once it reaches the original data once, when that data is needed again, it just takes the cached copy.