Grandfather-father-son backup is a common rotation scheme for backup media, in which there are three or more backup cycles, such as daily, weekly and monthly.
The daily backups are rotated on a daily basis using a FIFO system as above. The weekly backups are similarly rotated on a weekly basis, and the monthly backup on a monthly basis.
In addition, quarterly, half-yearly, and/or annual backups could also be separately retained. Often some of these backups are removed from the site for safekeeping and disaster recovery purposes.