Definition
HOVER TAXI
Used to describe a helicopter/VTOL aircraft movement conducted above the surface and in ground effect at airspeeds less than approximately 20 knots. The actual height may vary, and some helicopters may require hover taxi above 25 feet AGL to reduce ground effect turbulence or provide clearance for cargo slingloads.
Source: FAA Pilot/Controller Glossary (verbatim from the Federal Aviation Regulations).