High speed milling is the same or similar to conventional CNC milling with the main difference being the machines are purpose built to spin at higher revolutions (typically from 20,000rpm to 60,000 rpm) and have very accurate machine control.
The other key technique of high speed machining is the ability to take very small cuts, but at high speed with a ball nose or bull nose cutter. Doing this reduces the height of the microscopic 'scollop' left in between each cutter pass resulting in a superior surface finish. Due to the high speed of operation, this can be accomplished in a time similar to regular CNC machining but with superior results.
High speed machining has excellent applications in fast production of rapid tooling and the machining of hard materials. Modern toolmaking also requires the milling of smaller and smaller micro moulding tools which require high speed machining techniques to produce.