What is this?

What is this? Is it a train or a tram?

"London Trams" is an arm of Transport for London, which manages the second generation of tram services within London, UK. Current and planned tram systems are:
Tramlink operates a three-route system in the area of South London around Croydon. An extension to Crystal Palace is currently proposed.
Cross River Tram is a proposed new system in Central London from King's Cross and Camden to Peckham and Brixton; however, this project is currently on hold for lack of funding.
A scheme called City Tram has been proposed by the City of London, linking Battersea and Hackney via Elephant and Castle and The City, but does not appear in any of TfL's transport plans.