Plain English Meaning
Instruments that work by sensing the pressure of moving air against the aircraft. The faster the aircraft flies, the harder the air pushes into a small forward-facing tube, and that pressure is converted into readings the pilot can use.
Full Definition
A category of flight instruments that operate by measuring the pressure produced by the aircraft's motion through the air. These instruments compare the ram (impact) air pressure entering a forward-facing pitot tube with the static (still) air pressure from a static port, and use the difference to display airspeed, or use related pressure measurements to display altitude and vertical speed.
Context Anchor
Seen in instrument training when studying the and the that supplies it.