Revolving credit stays open. As you repay what you used, that amount becomes available again, and the account runs until the lender closes or renews it. Business lines of credit and business credit cards both work this way.
A term loan or a merchant cash advance is the opposite: a single amount repaid on a schedule. To get more money, you need a new deal.
Revolving credit is reviewed on a cycle, often yearly. The lender can lower or freeze the limit if your revenue drops or your account shows new risk, so treat an unused limit as available but not guaranteed. Keep a separate plan for a true emergency, such as a walk-in cooler that dies in July.