Plain English Meaning

Something is blocking the small opening on the airplane that lets outside air pressure into the instruments. When that happens, the altitude, climb/descent, and airspeed gauges stop showing the right numbers.

Full Definition

A condition in which the static port or static line — the source of outside, undisturbed air pressure used by the pitot-static instruments — becomes obstructed, typically by ice, water, insects, or debris. With the static source blocked, the altimeter, vertical speed indicator, and airspeed indicator can no longer outside air pressure, causing each to incorrect or frozen readings.