Which of the following defines 'temperature'?

The correct understanding of 'temperature' relates to the concept of how hot or cold an object is, which is fundamentally tied to the kinetic energy of its molecules. Temperature is defined as the measure of the average kinetic energy of the particles in a substance. Therefore, the speed at which molecules move is directly related to this average kinetic energy; higher speeds indicate higher temperatures, while lower speeds suggest lower temperatures.

This definition provides a clear relationship between molecular motion and the concept of temperature, making it a crucial element in understanding thermal energy and its effects on matter. The other choices do not accurately capture the essence of temperature. For instance, the amount of heat absorbed by a substance is more akin to heat flow or energy transfer rather than a measurement of its intensity, while heat capacity refers to the ability of a substance to hold heat, which is different from temperature itself.