Puerto Rico, also known as the Commonwealth of Puerto Rico, is a territory or colony of the United States in the Caribbean Sea. It has almost 4 million (4,000,000) people. It is the 169th largest sized country in the world in amount of land. Its political system is based on a republican system.he currency (money) used is the United States dollar. Puerto Rico means rich port in Spanish. The Commonwealth of Puerto Rico includes the largest, main island and a number of smaller islands, including Mona, Vieques, and Culebra.