Source : Webster's Revised Unabridged Dictionary (1913)

Lowland \Low"land\, n.
   Land which is low with respect to the neighboring country; a
   low or level country; -- opposed to {highland}.

   {The Lowlands}, Belgium and Holland; the Netherlands; also,
      the southern part of Scotland.

Source : WordNet®

lowland
     n : low level country [ant: {highland}]

lowland
     adj : of relatively low or level country [ant: {upland}]