Source : Free On-Line Dictionary of Computing

mmap
     
        The {Unix} {system call} which establishes a mapping between a
        range of addresses in a user process's address space and a
        portion of some "memory object" (typically a file, one of the
        special "devices" /dev/mem or /dev/kmem or some
        {memory-mapped} peripheral).  This allows the process to
        access a file at random byte offsets without using the seek
        {system call} or to access physical addresses or {kernel}'s
        {virtual address} space.  It can also be used as an
        alternative to writing a {device driver} since it is usually
        simpler to code and faster to use.
     
        (1995-02-14)