Definition - What does Synthetic Backup mean?
A synthetic backup is the process of utilizing the full backup of a file, and then modifying that file with one or more incremental backups. The first incremental backup is only created from changed data since the full backup; later incremental backups consist only of changed data from the last full backup. It is called a synthetic backup because it was not created from original data, but instead was created from two or more files merged, or synthesized, by the backup application.
Techopedia explains Synthetic Backup
Synthetic Backups are used when time or the system does not allow a full backup. Applications performing Synthetic Backups are not limited to single computer files. They can be used to backup entire folders or the contents of entire hard drives.
The purpose of a synthetic backup is to perform rapid backups and reduce the cost and time for data restoration.