Plain English Meaning
A small probe sticking out of the aircraft that measures the air rushing at it and the still air around it, with a built-in heater so ice cannot plug it up.
Full Definition
A combined pitot-static probe fitted with an internal electrical heating element that prevents ice from blocking the ram-air inlet and static ports during flight in visible moisture or cold conditions. It senses both impact (ram) air pressure for airspeed indication and static (ambient) air pressure for the altimeter, vertical speed indicator, and airspeed indicator, while the heater keeps the sensing openings of ice.