I am tremendously confused about the exact difference between thermal energy and internal energy and this confusion is largely due to the fact that even some of the most credible sources seem to contradict each other as illustrated here:
My copy of "Resnick Halliday" states the following:
"Thermodynamics is the study and application of thermal energy(often called the internal energy) of systems".
But on this Wikipedia page, the following has been stated:
"Thermal energy would ideally be the amount of heat required to warm the metal to its temperature, but this quantity is not well-defined, as there are many ways to obtain a given body at a given temperature, and each of them may require a different amount of total heat input. Thermal energy, unlike internal energy, is therefore not a state function."
(I am also confused about the fact that thermal energy is a path function; so, it is not defined for equilibrium states? If it is not possible to answer this question as well, I will post it separately)
Most people seem to think that the inherent confusion leading to this doubt is a confusion between the terms "heat" and "internal energy" (Eg: this question) but no, I fully understand that heat is not something that a system "holds" but is actually energy in transit and that it is NOT defined for an equilibrium state just as work is not defined for the same.
I know that a molecule can possess many types of energy (vibrational, translational, rotational etc.) and that the sum of these energies is defined as the internal energy of the system. Where then, does thermal energy come into the picture? Is it the same as internal energy since the internal energy of a system is technically zero at absolute $0K$? Some websites loosely state that it is the "jiggliness" of the atoms/molecules that constitute the thermal energy of the system. What are they trying to say?!
As you can see, I am in dire need of help. Please share your insights and also, keep in mind that I have only just graduated high school.
Edit: In another page, the same book defines thermal energy as follows;
"It is an internal energy that consists of the kinetic and potential energies associated with the random motions of the atoms, molecules and other microscopic bodies within an object."
So, it is not only the K.E but also the P.E associated with the moving constituents. Other types of energy within the system are those from chemical bonds etc, correct? Please correct me if I am wrong.
Much thanks in advance :) Regards.