Heat thermal energy is a measurement of the amount of energy imparted through the heat of a particular object. To understand this concept, it is important for one to understand that heat is in itself a form of energy. Thermal energy increases the movement of the atoms within a particular substance, which in turn heats it up and causes other effects, such as expansion of increased reactivity. The term "heat thermal energy" essentially means the same as heat energy or thermal energy, and the study of thermodynamics looks into the properties of heat and how it behaves.
At an atomic level, heat has a profound effect. If a pot of cold water was put over a hob, the heat imparted by the flame underneath the pot would increase the temperature of the pan, and that would increase the temperature of the water. As the temperature of the water increases, the atoms that make up the water start to move more rapidly, eventually literally jumping out of the liquid as steam. When the water is boiling, the atoms have been given enough heat thermal energy to literally escape the liquid and become a gas. In solids, heat causes the atoms to vibrate, which in turn causes them to expand to make room for the wiggling atoms.
Collisions between atoms are basically the cause of most chemical reactions, and those collisions are what many scientists believe led the Earth to exist. The speed at which the atoms are moving increases the likelihood that collisions will take place, essentially like the chance of two cars colliding being greater than the odds of two snails walking into each other. Heat thermal energy is known to increase the speed at which atoms move, which means that it also increases the speed of chemical reactions. This means that if a person wants to dissolve something such as a stock cube, increasing the heat of the solution into which it is being dissolved will increase the rate of dissolution. The energy from the heat is transferred to the atoms, which makes them more likely to react.
Generally speaking, heat thermal energy moves as a result of temperature differences between two systems. In the boiling water example, the heat of the fire transfers to the pan and the water because they are colder than the flame. If the heat of two separate systems was equal, no energy transfer would take place. Within a single closed system, the second law of thermodynamics states that all things tend toward entropy, or disorder. This means that dropping an ice cube into a hot cup of coffee causes the coldness from the ice cube and the heat from the cup to mingle together and create a warm mixture.