The Collaborative International Dictionary of English v.0.48:

Emigration \Em`i*gra"tion\, n. [L. emigratio: cf. F.
   ['e]migration.]
   1. The act of emigrating; removal from one country or state
      to another, for the purpose of residence, as from Europe
      to America, or, in America, from the Atlantic States to
      the Western.
      [1913 Webster]

   2. A body emigrants; emigrants collectively; as, the German
      emigration.
      [1913 Webster]

WordNet (r) 3.0 (2006):

emigration
    n 1: migration from a place (especially migration from your
         native country in order to settle in another) [syn:
         emigration, out-migration, expatriation]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

EMIGRATION. The act of removing from one place to another. It is sometimes
used in the same sense as expatriation, (q.v.) but there is some difference
in the signification. Expatriation is the act of abandoning one's country,
while emigration is, perhaps not strictly, applied to the act of removing
from one part of the country to another. Vide 2 Kent, Com. 36.