Mean number of arrivals per time period

Mean number of people or items served per time period

Average number of units $($customers$)$ in the system $($waiting and being served$)$

Average time unit spends in the system $($waiting time plus service time$)$

Average number of units waiting in the queue

Probability $($P$)$ that an average time unit spends waiting in the queue

Utilization factor $($h$)$ for the system

Probability of $0$ units in the system $($i$.$e$.$ the service unit is idle$)$

Probability $($P$)$ of more than k units in the system, where k is the number of units in the system