Source : Free On-Line Dictionary of Computing

PackIt
     
         A file format used on the {Apple
        Macintosh} to represent collections of Mac files, possibly
        {Huffman} compressed.  Packing many small related files
        together before a {MacBinary} transfer or a translation to
        {BinHex} 4.0 is common practice.
     
        (1994-11-30)