A business or a process is described as carbon neutral if it doesn't add to the net amount of CO2 in the atmosphere. This can be achieved either by emitting no CO2 to begin with - by using only renewable energy, say - or by 'offsetting' emissions (a controversial issue) which means compensating for emissions by another action which might reduce atmospheric CO2, such as planting trees. In practice, it is impossible for a person to live in an entirely carbon neutral way because even if you cut out energy consumption derived from fossil fuels, most products and services people rely on will have embodied emissions.