The term "temperature difference" refers to the variation in temperature between two different points or objects. It is usually measured using a thermometer and can be expressed in degrees Celsius, Fahrenheit, or Kelvin, depending on the specific context. Temperature differences are important because they can affect the behavior of materials, as well as biological systems such as human bodies. For example, when two objects have different temperatures, heat will flow from the warmer object to the cooler one until both reach the same temperature, which is described by the principle of thermal equilibrium. In summary, "temperature difference" refers to how much hotter or colder an object or space is compared to another reference point, and it plays a crucial role in understanding heat transfer and energy balance in various systems.