A medium-capacity system (MCS), also known as light rapid transit or light metro, is a rail transport system with a capacity greater than light rail, but less than typical heavy-rail rapid transit. MCS's trains are usually 1–4 cars. Most medium-capacity rail systems are automated or use light rail type vehicles.

Rapid transit or mass rapid transit (MRT), also known as metro, is a type of high-capacity public transport that is generally built in urban areas. A rapid transit system that primarily or traditionally runs below the surface may be called a subway, tube, or underground. Unlike buses or trams, rapid transit systems are railways, usually electric, that operate on an exclusive right-of-way, which cannot be accessed by pedestrians or other vehicles. They are often grade-separated in tunnels or on elevated railways.