Wikipedia
Maximum rate of oxygen consumption as measured during incremental exercise
Summary
V̇O2 max (also maximal oxygen consumption, maximal oxygen uptake or maximal aerobic capacity) is the maximum rate of oxygen consumption attainable during physical exertion. The name is derived from three abbreviations: “V̇” for volume (the dot over the V indicates “per unit of time” in Newton’s notation), “O2” for oxygen, and “max” for maximum and usually normalized per kilogram of body mass. A similar measure is V̇O2 peak (peak oxygen consumption), which is the highest rate attained during a session of submaximal physical exercise. It is equal to, or less than, the V̇O2 max. Confusion between these quantities in older and popular fitness literature is common. The capacity of the lung to exchange oxygen and carbon dioxide is constrained by the rate of blood oxygen transport to active tissue.