Heat transfer is the movement or flow of heat energy. Heat transfer is often used to describe the dissipation of heat energy from one location to the surrounding environment. It is governed by two main properties. The first property is temperature, which is the amount of thermal energy available. The second property is the flow of this thermal energy.
In terms of molecules, objects with higher temperatures have greater molecular agitation. In other words, the hotter something is, the faster its molecules move. Therefore heat transfer can also be viewed as the transfer of kinetic energy from one molecule to another.
Below is an amusing video that explains heat transfer in terms of home energy efficiency: