Plain English Meaning
The set of tubes and openings that lets the cockpit instruments measure the outside air pressure around the airplane. Three instruments depend on it: the one that shows altitude, the one that shows climb or descent rate, and the one that shows speed.
Full Definition
A system of tubing and ports that senses the still, undisturbed atmospheric pressure surrounding the aircraft in flight and delivers that pressure to the altimeter, vertical speed indicator, and airspeed indicator. The static port is positioned where the airflow is least disturbed by the aircraft's motion so the instruments receive an accurate sample of ambient air pressure.