Plain English Meaning
The pressure of the air being rammed into the small tube on the outside of the airplane as it moves forward. The faster the airplane flies, the harder that air pushes into the tube, and that push is what makes the airspeed indicator work.
Full Definition
The total pressure of the air entering the forward-facing opening of the pitot tube during flight, consisting of the static (ambient) air pressure plus the dynamic pressure caused by the aircraft's forward motion through the air. Pitot pressure is sensed by the airspeed indicator, which compares it against static pressure to display indicated airspeed.
Context Anchor
You encounter pitot pressure when studying the pitot-static system, especially airspeed indicator operation and pitot tube blockages.