Puerto Rico is a territory belonging to the United States. Historically, many parts of the current United States, such as Oregon and Missouri, were territories before statehood. The Philippines are an example of a former territory of the United States which is now an independent nation. There are also former territories which have become part of other nations. Territories and states are the two types of relationships available in the U.S. Constitution for land belonging to the United States. All land belonging to the United States is either a territory or a state.
U.S. territories belong to the United States but are not a state in the United States. The U.S. can therefore determine what parts of the constitution apply to a territory. The U.S. can admit a territory to the Union or grant it independence, something that usually follows a vote by the people of the territory. The United States can also cede a territory to another country, “cede” meaning to agree that the territory belongs to the other nation. Citizens of a territory generally have similar rights as citizens of the United States generally do, but the territory itself doesn’t have the rights of a state.
A piece of land belonging to the United States can only legally be a territory or a state.