A
train is called a
high speed train if its
maximum speed
in
normal operation is at least 200 kilometers per hour (125 mph).
Maglev
Despite decades of development, magnetic levitation (aka maglev)
technology permitting speeds above 500 km/h still remains to be
commercialized. A first baby step was taken in January 2003 when
Shanghai's 60-km Pudong Airport Transrapid express link opened; China has already signed a contract to extend the track some 300 km to Hangzhou and is considering building the 1500-km Beijing-Shanghai link
as maglev.
Dedicated Track
"Real" high speed trains run on dedicated track at speeds of
up to 300 km/h (186 mph). There are three families of high speed train technology, although the recent trend in Europe has been to build hybrids like the ICE 3 and Eurostar that can deal with multiple signaling systems.
InterCity Express (Germany)
Tilting
Tilting trains can tilt into a curve to allow higher speeds without
reducing passenger comfort. They run on minimally modified normal
track and can reach speeds of up to 250 km/h, although 200 km/h is the
usual maximum. Tilting technology has also been added to
dedicated-track high speed trains, namely the ICE-T and the TGV Pendulaire.
References
http://www.o-keating.com/hsr/
and a tip o' the hat to mawa