What does KEY denote in output of "list archivelog all"?

What does KEY denote in output of "list archivelog all"? What is that useful for?
RMAN> list archivelog all;

List of Archived Log Copies for database with db_unique_name DB112A
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Key     Thrd Seq     S Low Time
------- ---- ------- - ---------
67      1    14      A 06-JAN-14
        Name: /u01/app/oracle/product/11.2.0.2/db_1/dbs/arch1_14_836095779.dbf

68      1    15      A 06-JAN-14
        Name: /u01/app/oracle/product/11.2.0.2/db_1/dbs/arch1_15_836095779.dbf

69      1    16      A 07-JAN-14
        Name: /u01/app/oracle/product/11.2.0.2/db_1/dbs/arch1_16_836095779.dbf

70      1    17      A 07-JAN-14
        Name: /u01/app/oracle/product/11.2.0.2/db_1/dbs/arch1_17_836095779.dbf

71      1    18      A 07-JAN-14
        Name: /u01/app/oracle/product/11.2.0.2/db_1/dbs/arch1_18_836095779.dbf

72      1    25      A 19-JAN-14