Commercial bill is a bill of exchange used to finance the credit sales of firms. It is a short term, negotiable and self liquidity instrument. In case of goods sold on credit, the buyer is liable to make the payment on a specific date in future.
The seller could either wait till the maturity date or can draw a bill of exchange. When this bill is accepted by the buyer it becomes a marketable instrument and is called a trade bill. If the seller wants the funds before the maturity date, he can get the bill discounted from the bank. When a commercial bank accepts a trade bill it becomes a commercial bill.