1. the pressure exerted by the earth's atmosphere at any given point, being the product of the mass of the atmospheric column of the unit area above the given point and of the gravitational acceleration at the given point.
2. a value of standard or normal atmospheric pressure, equivalent to the pressure exerted by a column of mercury 29.92 in. (760 mm) high, or 1013 millibars (101.3 kilopascals). Also called barometric pressure. Cf. sea-level pressure.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.