A locomotive, also known as a train engine, refers to a vehicle that pulls or provides power for a train. There are many synonyms for locomotive, including engine, motive power, power plant, and power unit. Other terms include pusher locomotive, which is used to push trains up steep grades, and switcher locomotive, which is used for yard work and helping break up trains. Diesel-electric locomotives utilize diesel engines and electric generators to propel the wheels. Steam locomotives, on the other hand, are powered by steam that is created by heating water with coal or oil. No matter the type of locomotive, they all share the common goal of transporting passengers or cargo.