Short answers, pulled from the story.
A train is a series of connected vehicles that run along a railway track and transport people or freight. The word comes from the Old French trahiner, from the Latin trahere, meaning to pull or to draw. Most trains run on steel wheels over steel rails, whose low friction makes them efficient.
A steam locomotive built by British inventor Richard Trevithick powered the first ever steam train in 1804. Steam locomotives remained untried outside coal mines until the Stockton and Darlington Railway opened in 1825, where George Stephenson ran Locomotion No. 1.
Trains faced strong competition from automobiles and freight trucks beginning in the 1930s, which intensified after World War II, and air transport then became a rival for passenger trains. Large amounts of traffic shifted away, causing widespread service decline and the abandonment of many rail lines.
The first high-speed train was the Japanese Shinkansen, which entered service in 1964. High-speed trains generally start at a lower threshold of 200 km/h and operate at cruising speeds up to 355 km/h, usually on their own separate tracks.
According to the International Energy Agency, rail on average requires 12 times less energy and emits 7 to 11 times less greenhouse gases per passenger-kilometer than private vehicles and airplanes. In the United States as of 2008, railroads moved a ton of freight 436 miles per gallon of fuel, four times the efficiency of trucks.
Japan's L0 Series maglev holds the record for the fastest train ever, with a top speed of 374.7 mph, while the Shanghai maglev is the fastest commercial service at up to 431 km/h. Russia's Trans-Siberian Railway is the longest passenger service, running 5772 miles between Moscow and Vladivostok.