Store data so that they, or another application, can find it again later (databases) Remember the result of an expensive operation, to speed up reads (caches)
The boundary between a database and a cache is very, very fuzzy, and it is common that a database will be used as a cache.
Using a caching technology as your database is less common, but with appropriate backups, it can be a very good idea.
I would refer to master and secondary stores.
