In aviation, V-spees or Velocity-speeds are standard terms used to define airspeeds important or useful to the operation of aircraft, such as airplanes, gliders, autogiros, helicopters, blimps, and dirigibles. These speeds are derived from data obtained by aircraft designers and manufacturers during flight testing and verified in most countries by government flight inspectors during aircraft certification testing. Using them is considered a best practice to maximize aviation safety, aircraft performance or both.