What is free path? And what is mean free path?

(N/A) $1$. Free Path: The distance traveled by a gas molecule between two successive collisions is called the free path. During this interval,the molecule moves in a straight line with constant velocity.
$2$. Mean Free Path: The average distance traveled by a gas molecule between successive collisions is known as the mean free path. It is denoted by $\lambda$. If a molecule travels distances $\lambda_1, \lambda_2, \dots, \lambda_n$ between $n$ collisions,the mean free path is given by $\lambda = \frac{\lambda_1 + \lambda_2 + \dots + \lambda_n}{n}$.
Mathematically,it is expressed as $\lambda = \frac{1}{\sqrt{2} n \pi d^2}$,where $n$ is the number density of molecules and $d$ is the diameter of the molecule.