Great question. What is heat (and how is it different from temperature)?

You may already know that all materials are made out of atoms, the basic building blocks of matter. Atoms are constantly moving, vibrating, and jiggling around. This movement is very small, so small in fact, that we cannot perceive it – after all, we don't notice a coffee mug on a table move around! However, it's this small motion of atoms that results in what we call temperature, which is strongly interrelated to another physics concept, kinetic energy, the energy of motion. As atoms/molecules increase their temperature, their kinetic energy increases. More specifically, temperature is a measure of the average kinetic energy of the atoms/molecules in a material.

So then what on earth is heat? Very broadly, heat is a measurement of the total energy of a substance. That total energy is made up of not only kinetic energy but also of the potential energy of its atoms/molecules.

Thus temperature is not a measurement of energy, although it can tell us something about the average kinetic energy of the atoms/molecules in the material, while heat is indeed a measurement of the total energy of a material.

Again, what is heat? Heat is the total energy of a system.

Feel free to ask what energy is!