Definition
HIGH SPEED TAXIWAY
A long radius taxiway designed and provided with lighting or marking to define the path of aircraft, traveling at high speed (up to 60 knots), from the runway center to a point on the center of a taxiway. Also referred to as long radius exit or turn‐off taxiway. The high speed taxiway is designed to expedite aircraft turning off the runway after landing, thus reducing runway occupancy time.
Source: FAA Pilot/Controller Glossary (verbatim from the Federal Aviation Regulations).