Any wave that is required to fit irregularities at the boundary of a system or satisfy some impressed force within the system. The forced wave will not in general be a characteristic mode of oscillation of the system. It cannot be exhibited independently unless the system admits no free waves. A homogeneous incompressible fluid bounded by two rigid surfaces is an example of such a system. The gravity lee wave in the atmosphere is an example of mixed forced and free waves. See resonance, oscillation.