Boltzmann factor

In statistical mechanics and mathematics, a Boltzmann distribution (also called Gibbs distribution) is a probability distribution, probability measure, or frequency distribution of particles in a system over various possible states. The distribution is expressed in the form

${\displaystyle F({\rm {state}})\propto e^{-{\frac {E}{kT}}}}$

where ${\displaystyle E}$ is state energy (which varies from state to state), and ${\displaystyle kT}$ (a constant of the distribution) is the product of Boltzmann's constant and thermodynamic temperature.

...
Wikipedia