A tag is a text string that identifies a backup, either uniquely or as part of a group of backups. All Oracle Recovery Manager (RMAN) backups, including incremental backups, are labeled with a tag. For example, if you performed a full database backup every Saturday, then you could use the tag FULL_SAT to identify this backup.
You can use tags to refer to specific backups in RMAN commands. For example, you could issue a command to move the latest FULL_SAT backup to tape. If you do not specify a tag, then RMAN creates a unique tag automatically.
Because you can use tags to refer to different groups of backups, you can create different routines in your backup strategy that do not interfere with each other. When you schedule a backup job and give the job a name, the job name is the tag.