Source : Free On-Line Dictionary of Computing

blocked records
     
         Several {record}s written as a contiguous block on
        {magnetic tape} so that they may be accessed in a single I/O
        operation.  Blocking increases the amount of data that may be
        stored on a tape because there are fewer {inter-block gap}s.
        It requires that the tape drive or processor have a
        sufficiently large buffer to store the whole block.
     
        (1995-04-13)