"Fluid pressure" refers to the force that a liquid or gas exerts on its surroundings. It is the push or squeeze produced by the fluid due to its weight or motion. Full definition
Automatic transmissions use a valve body to shift gears using fluid pressures in response to speed and throttle input. (en.wikipedia.org)
While a manual transmission requires the driver to manually change gear ratios, an automatic does this on its own through the use of fluid pressure. (transmissionrepairguy.com)
But increasing fluid pressure at depth reduces the friction along the fault, sometimes triggering an earthquake. (sciencedaily.com)