Source : Webster's Revised Unabridged Dictionary (1913)

Platen \Plat"en\, n. [F. platine, fr. plat flat. See {Plate},
   and cf. {Platin}.] (Mach.)
   (a) The part of a printing press which presses the paper
       against the type and by which the impression is made.
   (b) Hence, an analogous part of a typewriter, on which the
       paper rests to receive an impression.
   (c) The movable table of a machine tool, as a planer, on
       which the work is fastened, and presented to the action
       of the tool; -- also called {table}.

Source : WordNet®

platen
     n 1: work table of a machine tool
     2: the flat plate of a printing press that presses the paper
        against the type
     3: the roller on a typewriter against which the keys strike