Bills (notes in British English) are paper documents used as currency.
Bills are also proposed laws put before a legislature.
A bill is also another name for the beak of a bird.
When goods are pre-ordered or purchased without immediate payment, a bill is usually received some time later. In this context it is short for a bill of lading. Bills are issued on a regular basis for payment of prearranged services or for services rendered. eg. water bill, gas bill, credit card bill, restaurant bill.