An Etymological Dictionary of Astronomy and Astrophysics

A loosely bound grouping of O and B stars that typically stretches up to several hundred → light-years and may contain between a dozen and several hundred → O stars
and → B stars. The members of an OB association are young and of roughly the same age. OB associations dissipate in a few tens of millions of years.

See also: O and B, from spectral types; → association.