Plain English Meaning
Holding done by faster aircraft at higher altitudes. Because the aircraft is moving faster through the air, the holding pattern itself is bigger, the allowed speeds are higher, and the airspace set aside to protect the pattern is wider.
Full Definition
A holding pattern flown by aircraft operating at higher true airspeeds, typically turbojets and turboprops at higher altitudes, where ICAO standard holding speeds and larger protected airspace dimensions apply. Above 14,000 feet MSL, maximum holding speeds increase (up to 265 knots in some segments), and the holding pattern's protected airspace is larger to account for the wider turn radius and longer leg distances flown at high true airspeed.