Source : Free On-Line Dictionary of Computing

longitudinal parity
     
         An extra {byte} (or word) appended
        to a block of data in order to reveal corruption of the data.
        Bit n of this byte indicates whether there was an even or odd
        number of "1" bits in bit position n of the bytes in the
        block.  The parity byte is computed by {XOR}ing the data bytes
        in the block.  Longitudinal parity allows single bit errors to
        be detected.
     
        (1996-03-01)