Fokkerjet (and eff oh) have provided detailed and precise explanations.
Their descriptions however are true only for turbojet/turbofan powered aircraft that were certificated under FAR25 or CAR4b.
Turbopropellor and piston powered aircraft that were certificated under CAR4b are a slightly different story. For example, for these aircraft, V2 (takeoff safety speed) was achieved on the runway, prior to liftoff. In addition, the runway length requirements were scheduled with a 50 foot height requirement rather than 35 feet.