Overdraft
A bank facility that lets a current account go below zero up to an agreed limit, with interest on what you use.
An overdraft, or cash credit facility, is the commonest way businesses borrow working capital. The bank sets a limit; you draw on it when cash is short and pay it back as customers pay you, paying interest only on what is drawn.
It is meant for short gaps, not for losses. It is far easier to arrange while the business is doing well than in the week the money runs out.
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See also: Working capital, Current account