This phrase entered commercial language with the willingness of commercial clearing banks to make unsecured advances to customers. The applicant approaches the bank manager and, if the latter is satisfied with the applicant’s creditworthiness, is advanced a specified sum. Interest is added to the loan and the total is normally repayable in instalments over an agreed period. The rate of interest charged is usually higher than for overdrafts, because no security is demanded.
Reference: The Penguin Business Dictionary, 3rd edt.