A protectorate is a state that is protected by another, larger and stronger country based on an agreement between the protectorate and the protecting country. These were very common in the 19th century, especially in Africa and South Asia, when European countries would give protection to small states or places there. Often they also made an international trade agreement which restricted the trade of other foreign states.
The British Empire had many protectorates around the world. The first was The Protectorate of the Commonwealth of England in the 1660s. Later, Kuwait was a British protectorate from 1899 to 1961 and is now independent. Sikkim was a protectorate of India until 1975 and now is a state of India.