What is the difference between a client and an order giver?

The term "customer" means (in the commercial sense) the person or entity who makes the decision to purchase a good or service, occasionally or habitually, from a supplier.

The “principal” is in the legal sense the natural or legal person who takes the initiative of an operation.

In subcontracting law, the principal is the one who subcontracts a service or the completion of a task to a subcontracting company.