A transit procedure is being used to move goods from the country of dispatch through one or more countries. There is no need to declare the goods in each of the crossed countries as this procedure allows goods to enter the movement of free circulation throughout the union.
If you are part of the Common Transit Convention (CTC) you can benefit from the transit procedure. The Common Transit Convention (CTC) is an agreement designed for common procedures for the international transit of goods between the EU, EFTA, Turkey, the Republic of North Macedonia, Serbia and the UK.