Source : Free On-Line Dictionary of Computing

triple DES
     
         A {product cipher} which, like {DES}, operates
        on 64-bit data blocks.  There are several forms, each of which
        uses the DES cipher 3 times.  Some forms use two 56-bit keys,
        some use three.  The DES "modes of operation" may also be used
        with triple-DES.
     
        (1995-05-11)