A credit line, also called line of credit, is an arrangement in which a bank or vendor extends a specified amount of unsecured credit to a borrower for a specified time period.
Credit lines come in many forms. Some common examples of credit lines include term loans, overdraft protections, discounting, demand loans, etc. Credit lines also have very varied terms and conditions, including interest rates, repayment terms, credit limit, and whether it is unsecured or secured.
It is up to the borrower to decide when to tap or use the credit in a credit line. Unless the borrower withdraws money from the credit line, interest will not accumulate and the borrower will have no fees to pay (at least interest fees). Some credit lines, and most credit cards, make borrowers pay regular fees (i.e. annual fees). In the case of credit cards though, it is not uncommon that the fee be waived when demanded by a borrower, especially if the borrower threatens to cancel the card.