In English law. A writ by which the king might by a special prerogative, privilege a defendant from all personal and many real suits for one year at a time, and no longer, in respect of his being engaged in his service out of the realm. 3 Bl. Comm. 289. In former times the name “protection” was also given to a certificate given to a sailor to show that he was exempt from impressment into the royal navy. In mercantile law. The name of a document generally given by notaries public to sailors and other persons going abroad, in which it is certified that the bearer therein named is a citizen of the United States. In public commercial law. A system by which a government imposes customs duties upon commodities of foreign origin or manufacture when imported into the country, with the purpose and effect of stimulating and developing the home production of the same or equivalent articles, by discouraging the importation of foreign goods, or by raising the price of foreign commodities to a point at which the home producers can successfully compete with them.