Plain English Meaning
A small heat sensor placed in the exhaust pipe that tells the pilot how hot the burned gases coming out of the engine are. The pilot uses that reading to set the fuel-to-air ratio correctly.
Full Definition
A temperature-sensing device, typically a thermocouple, installed in the exhaust manifold or exhaust pipe of a piston engine to measure the temperature of the gases leaving a cylinder. The signal from the probe is sent to a cockpit gauge that the pilot uses to monitor combustion and to lean the fuel/air mixture for efficient operation.