Little's law is also known as lemma or Little's theorem. According to this law, the long term average number of customers that are present in a stable system denoted by N, is actually equal to the long term average arrival rate, denote by lemda, multiplied by long term average time period a customer spends in a system, which is denoted by T.
Mathematically it is expressed as:
This law can be applied everywhere around us. Just imagine a shop which has a single counter. It also has a browsing area. Now only one person can be at the counter at a time. None of the customers leave without buying anything. The system is denoted as:
Entrance -> Browsing ->Counter -> exit.
The Little's law can be applied to the system within the shop. Such as the counter and the queue.