Backup in desktop and enterprise systems has the meaning of copying and archiving of computer data  to a second medium (a disk or tape) so it may be used to restore the original in case the first medium fails by various events such as buggy software, data corruption, date deletion, hardware failure, malicious hacking, user error or other unforeseen events.

Backups have two distinct aims. The primary aim is to recover data after its loss, by data deletion or corruption. The secondary aim is to recover data from an earlier time, according to a user-defined data retention policy, typically configured within a backup application for how long copies of data are required.

In cloud computing the word backup has a different meaning and is usally meant online backup which is offered as service. The user has not interest which method is used for backup data since this procedure is seamless. During the process a copy of the data is sent over the network to an off-site server.

The servive is provided usually with a fee based on capacity, bandwidth or number of users.