A more thorough explanation:

A commercial set refers to a group of important documents that are needed when goods are being shipped from one place to another. These documents usually include:

• An invoice: This is a document that shows the details of the goods being shipped, such as the quantity, price, and total cost.
• A bill of lading: This is a document that shows that the goods have been loaded onto a ship or other form of transportation.
• A bill of exchange: This is a document that shows that the buyer has agreed to pay for the goods at a later date.
• A certificate of insurance: This is a document that shows that the goods are insured in case they are lost or damaged during shipment.

These documents are very important because they help to ensure that the goods are shipped and paid for correctly. For example, if the buyer doesn't pay for the goods, the seller can use the bill of exchange to force them to pay. If the goods are lost or damaged during shipment, the certificate of insurance can be used to make a claim and get compensation.

Another example of a commercial set is the documents required under a letter of credit. A letter of credit is a document that guarantees payment to the seller as long as they meet certain conditions, such as providing the correct documents. The documents required under a letter of credit are usually the same as those in a commercial set.