heat is energy transferred from one place to another place due to thermal contact even when the systems are at different temperatures. energy can be transferred by heat between object or regions within an object with different temperatures. heat flows spontaneously from a system of higher temperature to a system to a system of lower temperature. when two systems of different temperature come into thermal contact the hotter body gives to the colder body more thermal energy than it takes from it until their temperatures are equal which at that point they obtain a state of thermal equilibrium. human notions such as hot and cold are relative terms and are generally used to compare one system's temperature to another or its surroundings.