By radiation, heat propagates without leading to a movement of matter, only the mechanical energy waves or electromagnetic energy waves move. Heat radiation propagates through gases, often by air. Through convection, takes place a movement of substance, fluids, liquids or gas from bottom up and vice-versa. Hot particles become lighter and rise, their place being taken immediately by the cold particles. The hot particles now are far from the heating source, they release the heat and become cold and heavy again, going down to the heating source level. In this way the cycle continues.
In order to understand what the heat is, it is necessary to explain some introductory notions. The universe consists of matter. The matter exists in form of substance or physical field. Energy is a property of matter. There is movement because the energy exists. Energy travels faster or slower depending on the wave transmission method (the electric field, electromagnetic field, oscillating mechanical motion, etc.). The energy propagates through substance. The substance opposed to unidirectional motion of waves and it imprints an oscillatory movement to the particles that are component parts of the respective substance. These particles (that are part of the substance) can be: molecules, atoms, ions, or electrons). The oscillatory movement is applied to the particles in several directions. That energy is called “heat”.