Which of the following best defines temperature?

The definition of temperature as the average kinetic energy of particles in a substance is foundational in the study of thermodynamics and physics. Temperature measures how fast the particles of a substance are moving; the faster they move, the higher the temperature. This relationship allows temperature to serve as an indicator of heat energy within a material.

In other contexts, the total heat energy in a substance includes not just the average energy of movement (kinetic energy) but also the potential energy from the interactions between particles. This broader definition does not effectively capture the concept of temperature itself.

Similarly, the amount of energy lost during a phase change relates to how temperature can affect state but does not encapsulate what temperature fundamentally is. Finally, the rate of heat transfer in a system pertains to the dynamics of how thermal energy moves rather than the intrinsic measurement of temperature. Thus, considering these distinctions, defining temperature as the average kinetic energy of particles in a substance is accurate and precise.