As matter is heated kinetic energy is imparted to the charged particles that make up the structure of the material. The average kinetic energy of the particles is known as the thermal energy of the system.
In some fields the term "heat transfer" is used when describing the production of electromagnetic energy (i.e. radiation/light) by the process of heating. But this is simply looking at the concept of thermal radiation from a slightly different perspective and the terms really interchangeable.
Thermal Radiation and Black Body Systems
Black body objects are those that exhibit the specific properties of perfectly absorbing every wavelength of electromagnetic radiation (meaning that they would not reflect light of any wavelength, hence the term black body) and they also will perfectly emit light when they are heated.
The specific peak wavelength of light that is emitted is determined from Wien's Law which states that the wavelength of light emitted is inversely proportional to the temperature of the object.
In the specific cases of black body objects it is the thermal radiation that is the sole "source" of light from the object.
Objects like our Sun, while not perfect black body emitters exhibit such characteristics. The hot plasma near the surface of the Sun generates the thermal radiation that eventually makes it to Earth as visible light.
heat transfer (usually in engineering fields), black body radiation (thermal radiation is the mechanism by which black body objects radiate energy).
Every object with a non-zero temperature will emit thermal radiation, the specific wavelength of radiation will entirely depend on the exact temperature of the object. In most cases the emitted radiation is not optical and therefore not visible to the naked eye.
The most common example of heat transfer in the field of astronomy is by that of stars, particularly our Sun. The surface temperature of our central star (roughly 6,000 degrees Celsius) is responsible for the production of white optical light that reaches Earth. (The Sun appears yellow due to atmospheric effects.)
Other common examples of thermal radiation include the coils on a stove top when they are heated, and even the infrared emission from the human body.