sound pressure

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The varying difference, at a fixed point in a given medium, between the pressure caused by a sound wave and either atmospheric pressure or the average pressure of the medium.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the difference between the instantaneous pressure at a point in a sound field and the average pressure at that point