Plain English Meaning
A small heater inside the airspeed sensor that stops it from icing up. The pilot turns it on with a switch in the cockpit, usually before flying through clouds, rain, or cold air.
Full Definition
An electrical heating element built into the pitot tube that prevents or removes ice blockage of the tube's ram-air inlet and drain holes, keeping the airspeed indicator working in visible moisture or freezing conditions.
Context Anchor
Seen on cockpit switches and checklists, especially before in cold, wet conditions or when icing is possible.