What is the relationship between the second law of thermodynamics and entropy?

Second law of thermodynamics tells about the degradation of energy caused due to entropy generation during heat transfer between system & surrounding through a finite temperature difference.

The entropy is a property of thermodynamic system which is measure of randomness in a system. The change in entropy is caused due to internal as well as external dissipative effects. The change in entropy of the universe is always non-negative i.e.

Hence, if there is entropy generation, there is degradation of energy.

The second law of thermodynamics states that the total entropy of an isolated system always increases over time, reaching a maximum at equilibrium. Entropy is a measure of the system's disorder or randomness. The law implies that natural processes tend to move towards increased disorder and randomness, resulting in a higher overall entropy.