Movement of out of an area.
Emigration can be treated similarly to deaths in terms of a popuation's dynamics. That is, it represents a loss of individuals by a population.
Like deaths, a population's (or density) within a given area can be reduced to zero via emigration, though obviously with different consequences so far as the population itself is concerned.
See also migration as defined in a sense as well as as defined more generally. Contrast with immigration.