Entropy: In an isolated system, entropy always increases according to the second law of thermodynamics.
Thermal Equilibrium: This is a state where all parts of a system have the same temperature. In an isolated system, thermal equilibrium will eventually be reached as there's no energy exchange with surroundings.
Conservation of Energy: This principle states that energy cannot be created or destroyed but only changed from one form to another. It applies perfectly to an isolated system since no energy enters or leaves it.