Radiation in the form of infrared light or infrared radiation is a type of energy thats invisible to the human eye but feels warm to the human body. Almost all objects in the universe emit some level of IR radiation. Even ice emits infrared radiation. The sun is the most obvious source of infrared radiation. Objects that have a temperature even if it is zero degrees emit this type of energy.
The existence of infrared light was discovered by humans in the 19th century but we have only recently begun to grasp its significance.
Animals have been exposed to infrared radiation for eons a fact that is truly astonishing. Although they may not know what it is or what it is called they sure know how to use it. Many species use IR to detect the heat source of a body in the dark when they cannot see it to navigate the world or to hunt for food.