Thermal radiation was electromagnetic radiation generated by the thermal motion of particles in matter.
In 1996 on Earth, the time traveling Tuvok from 2373 claimed that thermal and ultraviolet radiation were at hazardous levels. He refused to take off his shirt and risk dermal dysplasia. (VOY: "Future's End")
In 2366, while the USS Enterprise-D entered standard orbit of Gamma Hromi II, Lieutenant Commander Data detected life readings from the planet surface, and several small areas of thermal radiation and carbon dioxide emissions indicative of combustion; campfires. (TNG: "The Vengeance Factor")