Gas is one of states of matter. A gas mixture contains a variety of pure gases much like the air. What distinguishes a gas from liquids and solids is the vast separation of the individual gas particles. This separation usually makes a colorless gas invisible to the human observer. The interaction of gas particles in the presence of electric and gravitational fields are considered negligible.
Vapour is a substance in the gas phase at a temperature lower than a certain temperature called critical temperature. The vapour can be condensed to a liquid or to a solid by increasing its pressure without reducing the temperature.