Plain English Meaning
A simple temperature gauge that works by using two metals stuck together. The metals bend as they warm or cool, and that bending moves a needle to show the temperature.
Full Definition
A thermometer that measures temperature using a sensing element made of two different metals bonded together. Because the two metals expand at different rates when heated, the bonded strip bends as temperature changes, and that movement is mechanically linked to a needle on a dial to display the temperature. In light aircraft it is commonly used as the Outside Air Temperature (OAT) gauge, with the sensing probe protruding through the windshield or fuselage into the airstream.
Context Anchor
Seen in discussions of the outside air temperature gauge on an aircraft .