(acoustics) the pressure exerted on a surface normal to the direction of propagation of a sound wave WordNet 3.0 & Open English WordNet

Acoustic radiation pressure is the apparent pressure difference between the average pressure at a surface moving with the displacement of the wave propagation and the pressure that would have existed in the fluid of the same mean density when at rest. Wikipedia

Apparent pressure difference between the average pressure at a surface moving with the displacement of the wave propagation (the Lagrangian pressure) and the pressure that would have existed in the fluid of the same mean density when at rest Wikidata