An Etymological Dictionary of Astronomy and Astrophysics

A simplification in the equations of → hydrodynamics that treats the density as constant except in the → buoyancy term. This approximation is motivated by the fact that when pressure and temperature differences in a flow are small, then it follows from the thermodynamic → equation of state that a change in the density is also small.

See also: Named after Joseph Valentin Boussinesq (1842-1929), a French physicist
who made significant contributions to the theory of hydrodynamics, vibration, light, and heat; → approximation.