A tram (in North America streetcar or trolley) is a train that runs on tramway track on public urban streets; some include segments of segregated right-of-way.[1][2] The lines or networks operated by tramcars as public transport are called tramways or simply tram/streetcar. Many recently built tramways use the contemporary term light rail. The vehicles are called streetcars or trolleys (not meaning trolleybus) in North America and trams or tramcars elsewhere. The first two terms are often used interchangeably in the United States, with trolley being preferred in the eastern US and streetcar in Canada and the western US. In parts of the United States, internally powered buses made to resemble a streetcar are often referred to as "trolleys". To avoid further confusion with trolley buses, the American Public Transportation Association (APTA) refers to them as "trolley-replica buses". In the United States, the term tram has sometimes been used for rubber-tired trackless trains, which are unrelated to other kinds of trams.

With more than 14,000 units built, Tatra T3 is one of the most widely produced tram models in history.
14,991 KTM-5 tram vehicles were manufactured in Russia from 1969 to 1992.
Alstom tram in Tours crossing the Loire river.
Siemens tram in Almada near Lisbon.

Tram vehicles are usually lighter and shorter than main line and rapid transit trains. Today, most trams use electrical power, usually fed by a pantograph sliding on an overhead line; older systems may use a trolley pole or a bow collector. In some cases, a contact shoe on a third rail is used. If necessary, they may have dual power systems—electricity in city streets and diesel in more rural environments. Occasionally, trams also carry freight. Trams are now commonly included in the wider term "light rail",[3] which also includes grade-separated systems. Some trams, known as tram-trains, may have segments that run on mainline railway tracks, similar to interurban systems. The differences between these modes of rail transport are often indistinct and a given system may combine multiple features.

Ultra Light Rail ULR trains & trams are a developing light weight rail type,[4] around <5T/axle (empty), for use in smaller cities and towns to replace main bus routes eg. Coventry Very Light Rail,[5] ULR Partners future-light-rail[6] or lower use branch train lines. They may be normal trams,[7] rail motor sized and/or smaller modular units capable of platooning.[8] They offer all the advantages of traditional trams but their lower weight, prefabricated beam type tracks[9][10][11] offer the possibility of avoiding costly services diversions, lightweight OHL Over Head Lines[12] and/or onboard power options eg. hydrogen, biomethane, battery, may mean reduced/eliminated OHL. Thus installation costs may be lower than traditional trains and trams.

One of the advantages over earlier forms of transit was the low rolling resistance of metal wheels on steel rails, allowing the trams to haul a greater load for a given effort. Problems included the high total cost of ownership of horses. Electric trams largely replaced animal power in the late 19th and early 20th centuries. Improvements in other vehicles such as buses led to decline of trams in the mid 20th century. However, trams have seen resurgence in recent years. In 2014, the Aubagne tramway in Southern France became the first tram system in the world not to charge fares.[13]