A group of individuals of the same kind, or the same species, occupying a given area.

One of two groups that stars and stellar clusters can be divided into, depending on age, position in space, and chemical composition: Population I stars are relatively young, are very luminous, and belong to the spiral arms of galaxies. Typical members are O-type stars, Delta Cephei stars, and open clusters.

One of two groups that stars and other celestial bodies can be divided into: Population II stars are typically old. They are metal-deficient, are found in the center of the galaxy, and also follow highly elliptical orbits that take them far from the galactic disk.

Typical Population II members are long-period variable stars, globular clusters, and type II cepheid variables.