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