Plain English Meaning
A pitot tube with a built-in electric heater that keeps it from icing up so the airspeed indicator keeps working in cold or wet conditions.
Full Definition
A pitot tube assembly fitted with an internal electric heating element designed to prevent ice from forming in or blocking the tube during flight in visible moisture or at low temperatures. The heater warms the metal of the pitot head so that water droplets and ice crystals do not accumulate and obstruct the ram-air opening or drain holes, which would cause the airspeed indicator to read incorrectly.
Context Anchor
Seen in pitot-static system diagrams, - discussions, checks, and when using the before or during flight in cold, wet conditions.