Thermal Radiation is the radiation that is emitted from the surface of an object due the the temperature of it.

It is part of the electromagnetic spectrum. For this reason matter is not required for heat to travel, unlike conduction and convection, and it can pass through a vacuum.

Radiation is emitted by everything above absolute zero

Some surfaces absorb radiation better than others. Dull black surfaces absorb much more radiation than shiny silver surfaces. A shiny silver surface is a good reflector.

Some surfaces are also emit radiation better than others. A dull black surface will emit more radiation than a shiny silver one.