In commerce, a third-party source means a supplier (or service provider) who is not directly controlled by either the seller (first party) nor the customer/buyer (second party) in a business transaction.[1] The third party is considered independent from the other two, even if hired by them, because not all control is vested in that connection. There can be multiple third-party sources with respect to a given transaction, between the first and second parties. A second-party source would be under direct control of the second party in the transaction.[2]
In information technology, a third-party source is a supplier of software (or a computer accessory) which is independent of the supplier and customer of the major computer product(s).
In e-commerce, 3rd party (3P) source refers to a seller who publishes products on a marketplace, without this marketplace to own or physically carry those products. When an order comes in, a 3P seller has the item on hand and fulfills it. An example of 3P sellers are merchants participating in Amazon's FBM program.[3]