The term 'Subway System' is used to refer to a variety of transportation systems, including METRO, UNDERGROUND, and rapid transit. METRO is a form of public transport consisting of a network of high-speed trains or buses operating on designated routes. UNDERGROUND refers to a system of tunnels and stations that are used for public transportation, usually in urban areas. Rapid transit is a form of public transportation that operates at higher speeds than regular buses or trains. All three of these systems are commonly referred to as subway systems.