“Big Boy” locomotives A class of steam locomotives built in the US in the 1940s. At 40 metres (131 feet) long and 600 tonnes, Big Boys were the largest, heaviest and most powerful steam locomotives ever.

Boiler A tank containing water that, when heated, evaporates into steam. As more steam collects, its pressure builds, and it is fed to cylinders, where it pushes pistons that power the driving wheels.

Driving wheels The wheels that drive a locomotive along. The sliding motion of pistons in the engine moves the wheels around via a system of connecting rods.

Firebox An area where coal is burned to heat the boiler. A person known as a stoker or fireman, supplied the firebox with coal.

Funnel A tall, hollow column at the front of a steam locomotive. Also known as a chimney, it sends smoke from the engine and steam from the cylinders into the air above the train.

Gauge The distance between the two rails making up a railway track.

Locomotive A self-propelled vehicle, found at the front or back of a train, and used for pushing or pulling it.

Mallard The fastest ever steam locomotive. The Mallard set a speed record of 201 km/h (125 mph) in 1938.

Mountain railway A railway built on mountain slopes. Some very steep railways, called rack and pinion railways, have cog-shaped wheels (pinions), that grip on to a toothed rail (rack) between the tracks.

Narrow-gauge railway A railway with a gauge of less than 1.5 metres (4.9 feet). Narrow-gauge railways can have tighter bends than standard-gauge railways, for example around mountain slopes, and can fit through narrow tunnels, such as in mines.

Orient Express A long-distance passenger rail service, originally travelling from Paris to Istanbul. It started service in 1883, offering passengers first-class luxury. It still travels part of the route today.

Pilot A device, also known as a “cowcatcher”, mounted on the front of a locomotive and used to clear objects from the track.

Rocket The steam locomotive built by George Stephenson. In 1829 the Rocket won a competition for the best steam locomotive. It travelled at speeds of 47 km/h (29 mph). Its design was used for all later steam locomotives.

Signal A device beside a railway line that shows train drivers whether the track ahead is clear. Early signals used mechanical arms. Modern signals are mostly controlled by computers.

Stephenson, George (1781–1848) British engineer who built the first public railway line to use steam locomotives. The gauge George Stephenson used is now the “standard gauge”, used in 60% of the world’s railways.

Stockton and Darlington Railway The first steam passenger railway, which opened in England in 1825. Its trains were powered by the Rocket steam locomotive.

Stoker A machine used to supply an engine’s firebox with coal. Some could deliver as much as 22,000 kilograms (48,000 pounds) an hour.

Train A train is a vehicle, consisting of a locomotive and carriages, that runs on guide rails called a railway. The first trains were invented almost 200 years ago and driven by steam-powered locomotives, which use the energy produced by pressurized steam. Before the invention of trains, the fastest people could move across land was on horseback. The development of the railways enabled people and heavy goods to be transported more quickly and easily.

Trevithick, Richard (1771–1833) English engineer who built the first locomotive powered by a steam engine in 1804. Trevithick’s locomotive was used to haul trucks at an ironworks. It could pull up to 10 tonnes of iron.

Water tower A large container from which steam locomotives could refill their water, which was lost constantly as steam. Water towers were positioned beside tracks, at stopping places and depots.

Consultant: Chris Oxlade