What is Perfect gas, microscopic model?

A perfect gas (ideal gas) is a collection of $N$ molecules, treated as points of mass $m$, moving freely and at random — no interaction except brief collisions — in a container of volume $V$. At equilibrium the velocity distribution is isotropic and stationary; $n^* = N/V$ is the number density and $\langle v^2\rangle$ the mean square speed.