In business a line of credit or credit line is an arrangement/commitment by a bank or other creditor with a customer. The agreement specifies an amount that the customer can borrow or use in the future, assuming that the customer's financial condition is maintained.
For example, a company may arrange with its bank to borrow money as needed but never owe the bank in excess of $500,000. The agreement might specify that interest will be calculated by multiplying the prime rate times the loan balance.
In the U.S. many individuals have a home equity line of credit that allows them to borrow up to the amount of "the line."