1. A stress or force acting in any direction against resistance.
2. physics, physiology the force per unit area exerted by a gas or liquid against the walls of its container or that would be exerted on a wall immersed at that spot in the middle of a body of fluid:The pressure can be considered either relative to some reference pressure, such as that of the ambient atmosphere (imagined as on the other side of the wall) or in absolute terms (relative to a perfect vacuum).
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