...is just under red of the visible spectrum, hence "infra" red.
Most of the heat from objects near room temperature and below is in the infrared. Mostly from vibration or torsion of molecules, which are a big part of black body
Half of the sun's energy is infrared and heats the earth (527 / 1000 Watt per square meter at at sea level) .
Stars, dust between stars, Sun, Blackbody radiation, Heat
Heat seeking systems, ..
Fibre optics, networks, all kinds of communication, ..
Mobile phones, radar, TV, radio, remote controls, ..
Electronic photography, thermal efficiency analysis, environmental monitoring
Remote temperature sensing
Interaction with matter: