For atomic particles (protons, neutrons, electrons), their average velocity (almost never the same across a given sample, and less likely the larger the sample) is measurable, and we call that temperature. It’s a way to describe the total energy of a system. As it happens, we use that property for everything from steam turbines to cutting torches to deep freezers. It’s a simplified answer, but the engineering realities take into account many other properties and variables which relate to temperature in order to achieve the desired effects.
For atomic particles (protons, neutrons, electrons), their average velocity (almost never the same across a given sample, and less likely the larger the sample) is measurable, and we call that temperature. It’s a way to describe the total energy of a system. As it happens, we use that property for everything from steam turbines to cutting torches to deep freezers. It’s a simplified answer, but the engineering realities take into account many other properties and variables which relate to temperature in order to achieve the desired effects.