Action over-invoicing, which means that to increase fraudulently the price of a good or service.
A real service is made (or products are delivered), and an invoice inflated deliberately is paid by the customer, who is accomplice of supplier. The overpayment is returned to the customer in the form of liquid or various benefits.
The advantage of over-invoicing is obviously in return to allow "production" and discreet exit of illegal money. For example when the supplier and customer are accomplice and who get an agreement beforehand, one to increase the price of a service and the other to pay in order to retrocede him eventually in cash or in fringe benefits, which corresponds to the overpayment.