A table is said to be in First Normal Form (1NF), if all entries in it are scalar-valued i.e. no repeating elements.
A customer may order many products during one transaction. Hence, a particular order may have many entries for each of these products. The customer information, in this case gets duplicated each time.
To make the denormalized "customer_order" table to comply with 1NF, the repeating group of data elements, the customer names and address and the product names and cost are normalized into separate tables.
Three separate tables 'order', 'product' and 'customer' are created.