Source : Free On-Line Dictionary of Computing

Indexed Sequential Access Method
     
         (ISAM) An {IBM} file management system allowing
        records to be accessed either sequentially (in the order they
        were entered) or via an index.  Each index orders the records
        on a different key.
     
        ISAM was followed by VSAM ({Virtual Storage Access Method})
        and pre-dated {relational databases}.
     
        (2003-07-13)