What was an external tax in colonial America?

In colonial America, an external tax was a tax laid by the British Parliament to regulate trade and commerce in mercantilistic colonial America. Though opposed to an internal tax, which Daniel Dulany states in his Considerations on the Propriety of Imposing Taxes in the British Colonies, 1765 as a tax with "The single purpose of revenue," the colonies agreed to let Great Britain lay external taxes without their consent.