Plain English Meaning
It is the set of small air openings and tubes on the outside of the aircraft that feed three flight instruments: the one showing how fast you are going, the one showing how high you are, and the one showing how quickly you are climbing or descending.
Full Definition
The pitot/static system is the network of ports, lines, and instruments that uses outside air pressure to drive the airspeed indicator, altimeter, and vertical speed indicator. The pitot side measures ram air pressure from forward motion through a forward-facing tube, while the static side measures ambient air pressure through flush ports on the side of the aircraft. The instruments compare these two pressures to calculate airspeed, altitude, and rate of climb or descent.