There are 3 important E’s within the study of the thermodynamics

1) Equilibrium

2) Entropy

3) Energy

Entropy is that the extensive property of the system (depends on the mass of the system) and its unit of measurement is Joule per degree Kelvin. it's taken from the Greek word ‘tropee’ which implies transformation. Entropy is heat or energy change per degree Kelvin temperature. Entropy is denoted by "S".

The second law of thermodynamics says that entropy always increases with time.

See the video to understand the entropy by examples:

https://www.youtube.com/watch?v=YM-uykVfq_E

Find out more:

https://eic.rsc.org/feature/what-is-entropy/2020274.article