List backup in summary mode

I tried to find the meaning of the value in the list backup in summary mode. I looked through the Database Backup and Recovery Reference for 11gR2, but it didn't show me anything.

List of Backups
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Key     TY LV S Device Type Completion Time #Pieces #Copies Compressed Tag
------- -- -- - ----------- --------------- ------- ------- ---------- ---
1       B  0  A DISK        31-JUL-12       1       1       NO         WEEKLY-BACKUP
2       B  0  A DISK        31-JUL-12       1       1       NO         WEEKLY-BACKUP
3       B  0  A DISK        31-JUL-12       1       1       NO         WEEKLY-BACKUP
4       B  0  A DISK        31-JUL-12       1       1       NO         WEEKLY-BACKUP
5       B  F  A DISK        31-JUL-12       1       1       NO         TAG20120731T185551
6       B  F  A DISK        31-JUL-12       1       1       NO         TAG20120731T185559
7       B  A  A DISK        31-JUL-12       1       1       NO         WEEKLY-BACKUP