From the longer Wikipedia page [1]
Heathrow Terminals 2 & 3 railway station (also known as Heathrow Central) serves Terminal 2 and Terminal 3 (and formerly Terminal 1 before its closure in 2015) at London Heathrow Airport.
It is served by Heathrow Express trains direct to central London and Elizabeth line trains that stop at local stations. It is 14 miles 50 chains (23.5 km) down-line from London Paddington.
Travelcards from Transport for London are not valid on Express services from the station, although they are valid on the Elizabeth line. Passengers transferring between any of the terminals at Heathrow may use the trains free of charge.