the movement of persons from one country or locality to another | something that happens at a given place and time |
the periodic passage of groups of animals (especially birds or fishes) from one region to another for feeding or breeding | a phenomenon located at a single point in space-time; the fundamental observational entity in relativity theory |
(chemistry) the nonrandom movement of an atom or radical from one place to another within a molecule | a phenomenon that follows and is caused by some previous phenomenon |
a group of people migrating together (especially in some given time period) | a special set of circumstances |