Wiktionary defines a cache as “a store of things that will be required in the future, and can be retrieved rapidly.” A cache is a collection of temporary data that either duplicates data located elsewhere or is the result of a computation. Data that is already in the cache can be repeatedly accessed with minimal costs in terms of time and resources.

When a data element is requested from cache and the element exists for the given key, it is referred to as a cache hit (or simply, “a hit”).

When a data element is requested from cache and the element does not exist for the given key, it is referred to as a cache miss (or simply, “a miss”).

The authoritative source of truth for the data. The cache acts as a local copy of data retrieved from or stored to the system-of-record (SOR). The SOR is often a traditional database, although it might be a specialized file system or some other reliable long-term storage. For the purposes of using Ehcache, the SOR is assumed to be a database.