Source : Free On-Line Dictionary of Computing

reserved memory
     
         The address range 640-1024 {kilobytes} on an {IBM
        PC}, reserved for {BIOS}, {video cards}, and add-on cards.
        Depending on the configuration some of the address space may
        be unused in which case it can be used by {EMS} or {UMB}.
     
        (1996-01-10)