Much of the data stored on computers, such as the data stored in random access memory (RAM) and caches, is temporary and therefore referred to as "ephemeral" (which means transitory, or existing only briefly). These temporary, transient files are deleted as often as every few hours.
In computing, a "persistent data structure" is a data structure that always preserves the previous version of itself when it is modified. A data structure is partially persistent if all versions can be accessed but only the newest version can be modified. The data structure is fully persistent if every version can be both accessed and modified. If there is also a meld or merge operation that can create a new version from two previous versions, the data structure is called confluently persistent. Structures that are not persistent are called ephemeral.