Backup, or data backup, is the process of creating a copy of computer data and storing it elsewhere so that it can be used to restore the original after a data loss event. The purpose of backup is to protect against data loss due to equipment failure, data corruption, buggy software, malicious hacking, user error, or other unforeseen events. Backups can be used to recover data after its loss from data deletion or corruption, or to recover data from an earlier time. A backup strategy requires an information repository, which could be as simple as a list of all backup media or could include a computerized index, catalog, or relational database.

There are different ways to perform a backup, including copying files, making user-initiated backups and restores, and using backup software. The backup administrators primary initial task is to understand, define, and manage what data to back up and protect. The backup process is governed by predefined backup policies that specify how frequently the data is backed up and how many duplicate copies are required, as well as by service-level agreements (SLAs) that stipulate how quickly data must be restored.

Key concepts related to backup include Recovery Point Objective (RPO) and Recovery Time Objective (RTO), which are two of the most critical factors for planning backup and disaster recovery strategies. RPO refers to the amount of data that can be lost before it becomes unacceptable, while RTO refers to the amount of time it takes to recover data after a disaster.

In summary, backup is a critical process for protecting against data loss and ensuring business continuity. It involves creating a copy of computer data and storing it elsewhere, and can be performed in different ways depending on the backup strategy and policies in place.