Entropy is a concept introduced when dealing with

heat (engine) problem. It is closely related to energy

but not conserved.

The thermodynamic laws 2 and 3 are concerned with entropy.

Entropy is not yet scientifically matured, some disciplines have

their own definitions, so using it carelessly may cause many

confusions.

For example, humans can be considered open systems

with oxygen as input and walking, running or doing other works

as output. So the entropy for humans are always decreasing

no matter what you do because they are also

equal temperature system (Q / T).