Thermal energy, by definition, is energy that is derived from heat. This is a common science topic in the 3rd grade.
Within an object or substance, there are minuscule particles that can not be seen by the human eye, constantly moving and colliding. As the particles continue to speed up, moving faster and faster, so does the heat intensify and increase. I.e. The movement of particles and intensity of heat work in correlation with one another.
The term 'heat' is usually used in reference to transfer, that is to say that if thermal energy is exported from one object to another, that transition is what we refer to as heat. Terminology can sometimes be confused, since the word heat is essentially a verb, it is an active process. So it is important to use term correctly in referring to the process and not the outcome.
I hope this answers your question.