$1.$ Starting off with zero customers in the system: this is when there are no customers in the system none in the line or being served at any given time. In the bank in the afternoons between $12-2$ its pretty quiet and sometimes maybe no customers as everyone is either at work or on their lunch break.

$2.$ Average number of customers in the system: This is the number of customers waiting and being served. This depends on how long a teller takes with a customer and at what rate the customers come in$.$

$3.$ Average time a customer spends in the waiting line: This is the average amount of time a customer has to wait before they are helped.

$4.$ Average number of customers in a waiting line: This is the amount of customers that are waiting to be helped by the tellers.

$5.$ Average amount of time a customer spends in the system: this is the total amount of time a customer spends in the waiting line and while being served.