# Definition:Entropy (Physics)

## Definition

Entropy is a property of a thermodynamic system.

It quantifies the number $\Omega$ of microstates that are consistent with the macroscopic quantities that characterize the system.

The entropy of a system is equal to the expectation of the value:

$k \ln P$

where:

$k$ is a constant which relates the mean kinetic energy and absolute temperature of the system
$P$ is the coefficient of probability of the system.