Temperature is related to the random motion of atoms and molecules in a substance. More, specifically, temperature is proportional to the average "translational" kinetic energy of molecular motion. Molecules may also rotate or vibrate, with associated rotational or vibrational kinetic energy-- but these motions are not translational and don't directly affect temperature.
How well a solid object conducts heat depends on the bonding within its atomic or molecular structure. Solids built of atoms that have one or more "loose" outer electrons, which are free to carry energy by collisions throughout the metal. They are excellent conductors of heat and electricity for this reason.
The above paragraphs are from the book "conceptual physics by Hewitt". It is said that when we measure temperature by classical mercury thermometer what we measure is actually the average translational kinetic energy of the molecules within the substance. Thinking about the above paragraphs actually makes sense to me.
My Questions: Are there any free electrons in a block of wood or some other electrical insulators? If not, how do we define their temperatures if we cannot talk about translational motions within the body? And by the same logic, can't we measure the temperature of wood by a thermometer?