Recovery Window-Based Retention Policy ==>
RMAN does not consider any full or level 0 incremental backup as obsolete if it falls within the recovery window. Additionally, RMAN retains all archived logs and level 1 incremental backups that are needed to recover to a random point within the window.
Redundancy-Based Retention Policy==>
The REDUNDANCY parameter of the CONFIGURE RETENTION POLICY command specifies how many full or level 0 backups of each datafile and control file that RMAN should keep. If the number of full or level 0 backups for a specific datafile or control file exceeds the REDUNDANCY setting, then RMAN considers the extra backups as obsolete. The default retention policy is REDUNDANCY 1.