Bohr's second postulate: Electrons revolve only in those orbits where angular momentum is an integral multiple of \(\dfrac{h}{2\pi}\):

\(L = mvr = \dfrac{nh}{2\pi}\)

Here \(L\) is the angular momentum. This quantisation condition was the foundation of Bohr's model, later justified by de Broglie's wave theory (standing wave condition for electrons in orbit).