Source : Free On-Line Dictionary of Computing

upper memory block
     
         (UMB) Up to 64 {kilobytes} of the {expanded memory
        page frame} above the first 64 kilobytes.  The UMB can be used
        to store {TSR} programs or {device drivers} thereby freeing
        parts of the precious {conventional memory}.  The UMB is
        provided by special memory manager programs; many {EMM}s can
        provide UMB as well.
     
        (1996-01-10)