Thermodynamic probability

From Glossary of Meteorology

thermodynamic probability

Proportional to the number of equally likely states that a system may attain.

Boltzmann proposed that the entropy S and the thermodynamic probability W were proportional, and Planck subsequently showed that S = k ln W with k Boltzmann's constant. This result is of such fundamental significance in physics that it was carved as an adornment on Boltzmann's gravestone in Vienna.
See third law of thermodynamics.