Source : Webster's Revised Unabridged Dictionary (1913)

Migration \Mi*gra"tion\, n. [L. migratio: cf. F. migration.]
   The act of migrating.

Source : WordNet®

migration
     n 1: the movement of persons from one country or locality to
          another
     2: a group of people migrating together (especially in some
        given time period)
     3: (chemistry) the nonrandom movement of an atom or radical
        from one place to another within a molecule
     4: the periodic passage of groups of animals (especially birds
        or fishes) from one region to another for feeding or
        breeding