Rapid transit is a popular mode of transportation in many cities around the world. It is commonly known as the subway or metro, and it is an efficient way of moving people from one place to another quickly. There are many synonyms for rapid transit, including underground, tube, train, transit, rail, and mass transit. These words describe the same basic concept of trains or other forms of public transportation moving underground or on dedicated tracks to get people quickly and efficiently to their destinations. Whether you call it the subway or the tube, rapid transit is an important part of modern transportation infrastructure.