The Carnot cycle represents an idealized model of a heat engine that achieves the maximum possible efficiency for given reservoir temperatures.

The Carnot efficiency represents the maximum possible efficiency of a heat engine operating between two temperatures, $T_h$ (hot reservoir) and $T_c$ (cold reservoir).

The efficiency ($\eta$) of a heat engine measures how effectively it converts input energy into useful work.

Entropy is a measure of the disorder or randomness in a system. It quantifies the number of possible ways a system can be arranged.

Internal energy is the sum of kinetic energy and potential energy of a substance and is the result of the motion of the particles which make up the substance.