Queueing Models

In Kleinrock's book on Queueing Systems $($Volume $1),$ the well$-$known PollaczekKhinchin $($PK$)$ mean value formula on page $187$ states that the average number of customers in an M$/$G$/1$ system with FIFO service is:

$\frac{?}{\text{b}\text{a}\text{r}}(q)=+{}^2\frac{(1+C^2)}{2(1-)}$

where $C2$ is the squared coefficient of variation $($CV$)$ of the service time distribution.

$($a$)$ In simple English $($at most two sentences$),$ explain what the PK formula indicates about system occupancy.