Little's Law - is a law/theorem given by John Little which states that the average number of customers in a stable system, N, is equal to their average arrival rate, λ, multiplied by their average time in the system, T
N = λ x T
In more simplistic terms, Little's Law can be also be stated as
Items in Process (WIP or N) = Throughput (λ) x Lead Time (T)
This law is part of the Queuing Theory in Operations Research and is particularly useful in studying the length and waiting time in queues.
An application oriented question on the topic along with responses can be seen below. The best answer was provided by Priyer on 2nd January 2018.