RVSM stands for Reduced Vertical Separation Minimum. Under normal IFR rules, westbound flights fly at flight levels 310, 350, 390, etc. (4,000 ft separation). Eastbound flights fly at flight levels 330, 370, 410 (again 4,000 ft separation). Combining the westbound and eastbound flight levels, all aircraft should maintain a minimum of 2000 ft vertical separation (310, 330, 350, 370, 390, 410). Under RVSM rules, this 2000 ft vertical separation is reduced to 1000 vertical separation. This is already in place in the North Atlantic (NAT Track System), Pacific and within Eurocontrol (European) airspace. The purpose is to allow more traffic within the same airspace by reducing the amount of vertical separation. I hope this helps. sward