It's a Checkouts-group permission named Allow Confirm Payment. On an unpaid (pending) checkout, it controls whether a staff member sees and can use both the Confirm Checkout Payment button (marks the checkout as paid) and the Cancel Checkout button — so only authorized staff can settle or cancel an unpaid order. Without it, a user can still list and edit checkouts (if they hold those separate permissions), but neither button appears on an unpaid checkout.