The Free On-line Dictionary of Computing (30 December 2018):

address space

    The range of addresses which
   a processor or process can access, or at which a device can
   be accessed.  The term may refer to either physical address
   or virtual address.

   The size of a processor's address space depends on the width
   of the processor's address bus and address registers.

   Each device, such as a memory integrated circuit, will have
   its own local address space which starts at zero.  This will
   be mapped to a range of addresses which starts at some base
   address in the processor's address space.

   Similarly, each process will have its own address space,
   which may be all or a part of the processor's address space.
   In a multitasking system this may depend on where in memory
   the process happens to have been loaded.  For a process to be
   able to run at any address it must consist of
   position-independent code.  Alternatively, each process may
   see the same local address space, with the memory management
   unit mapping this to the process's own part of the
   processor's address space.

   (1999-11-01)