A letter of credit is a letter from a bank guaranteeing that a buyer (for example, your customer) will pay a seller (you) on time and for the correct amount. If the buyer cannot pay, then the issuing bank will be required to cover the full or remaining amount of the purchase. So, a letter of credit is like having a co-signer on a loan.
Letters of credit are often used in international trade, where factors such as geographical distance, differing laws in each country, and difficulty in knowing each party personally multiply the hazards businesses can face.
A letter of credit from your customers can reassure you of their ability to meet their financial transactional obligations, because the invoice covered by a letter of credit will be paid. It is a way to protect your cash flow and provide security in case something goes wrong with a transaction. It can be part of your credit management policy.