What is temperature and why are Kelvins used?

Temperature is the macroscopic effect of the average kinetic energy of the subatomic particles that compose a material. Kelvins are therefore used because they are the only true scale that connects to this property of temperature. Indeed, by taking the theoretical point where the temperature of any body is 0 K, we can stipulate that the particles of that body have 0 kinetic energy and thus they do not move or vibrate in any way.