Synthetic Full Backup: Incrementals Forever Explained

Incrementals Forever is the most efficient way to maintain a rolling series of recent backup points. Only a single full backup is required, all subsequent backups are incremental.

Old incrementals are merged into the full. This avoids the need to create a new full when purging old incrementals. The modified full is called a “Synthetic Full”.

https://knowledgebase.macrium.com/display/KNOW72/Scheduling+backups