RVSM - meaning?

[Rockhound]

I have a question: when the Hong Kong Radar controller asks a flight if it has RVSM (I believe it is) approval, what does he or she mean?
Thanks in advance for the info.
Rockhound

[HEATHROW DIRECTOR]

Reduced Vertical Separation MInima. Some aircraft are able to accept reduced vertical separation above FL290..

[Rockhound]

Heathrow Director and Mike Jenvey,
Thanks you very much.
Rockhound