I don't understand some of the charges on my invoice. Follow

Is it a user charge? 

Users who take call throughout the month are billed at the pre-determined contract rate. Admin users are free of charge on a 1:1 ratio between full on-call users and admin users. Occasional users are classified as users who only cover three days per month, or one weekend per month, or only covers one week per quarter and receive a discounted rate.