Saw it on a training video online and noticed it when listening to transmissions IRL, high speed climb.. It's a commonplace term now for heavies IRL as they're stall speeds are so high when heavy. The specific video I am referring to is explaining the Delta fuel dump over LA and they get up to nearly 370 knots at 7000. If anyone is interested, this is the video and time when SoCal automatically approves hsc:
https://youtu.be/JzKny78Eylg?t=148.
When requesting on Vatsim (I have tried twice so far), one time I was approved, saying it was a federal limitation, and the other one gave me a restriction of 270 knots which is hardly high speed. So is this not something we're simulating on Vatsim?