Metro systems, also known as Underground railways or subways, are a type of rapid transit system that operates primarily underground in urban areas. These systems use electric trains to transport passengers between stations, typically located in densely populated areas. The first Metro system was built in London in 1863, and since then, they have become a popular mode of transportation in many major cities around the world. Today, Metro Systems can be found in cities such as New York, Paris, Tokyo, and Beijing, with more being planned and constructed in the future.