Back-end:

This refers to a type of programme or process that is not directly accessed by a computer user. Often it will carry out its tasks independently of the front-end. For example, a user could request data from a database - not knowing that the data is refreshed on the back-end on a daily basis.

A "front-end" application is one that application users interact with directly, while a "back-end" application or programme serves indirectly in support of the front-end services.