The basic principle behind entropy is that in any energy transfer or transformation, there is a tendency for systems to move toward a state of disorder or chaos. In thermodynamics, it is often referred to as the measure of randomness or disorder within a closed system. Essentially, as energy is converted from one form to another, some energy becomes unavailable for doing useful work, leading to increased entropy. This principle underpins the second law of thermodynamics, emphasizing that energy transformations are inherently inefficient and contribute to the overall disorder of the universe.