VO2 stands for ventillary oxygen and represents the amount of oxygen you’re inhaling.
VO2 max represents the maximal rate at which you can use oxygen during exercise.
Three things to remember:
VO2 max is a common parameter of cardiorespiratory fitness because, as you become fitter, you become better at using oxygen to produce energy (your VO2 max increases).
Moreover, exercise intensity is often reported as a percentage of VO2 max based on the assumption that more intense exercise requires that you consume more oxygen to fuel your mitochondria (the power generators in your cells).
Nevertheless, higher VO2 max doesn’t always translate as better sports performance, because sports often involve moments when energy requirements are so great (the intensity is so high) that oxygen isn’t used to generate the required energy.