Student or Learner
It's just a card we issue to help us keep track of rentals and customer billing.
What is the meaning of 'billing' here? What is the difference between 'bill' and 'billing'?
If you give someone a bill, you are billing them. They have been billed.
If you bill (verb) a lot of people, you'd keep a record of this billing (noun), to check who has paid.
Billing (noun) is the process of issuing a bill.
Please take care of this month's billing = Please send out this month's bills.