While the principal market refers to the economic activity in which a good or service is offered, the complementary market covers goods and services directly related to those of the principal market. The supplementary contract therefore only exists to complement the main contract. In general, the products of the complementary market are linked to those of the main market by their technical characteristics.
This is the case, for example, with conditioners whose actions reinforce or complement those of the shampoo. We can also mention the heating devices and the different models of matching brushes or the laptops and USB keys, the wireless mice and all the other products related to them.