Did you learn it from Sam Leong ?
http://www.google.com.au/search?hl=...WQ9uCWBg&sa=X&oi=glossary_definition&ct=title
Definitions of migration on the Web:
* the movement of persons from one country or locality to another
* a group of people migrating together (especially in some given time period)
* (chemistry) the nonrandom movement of an atom or radical from one place to another within a molecule
* the periodic passage of groups of animals (especially birds or fishes) from one region to another for feeding or breeding
