Gas and vapour state of a matter are remarkably separated by a particular temperature of matter called critical temperature. If the matter is above the critical temperature it is in the gaseous state and when it is below the critical temperature, it is in the vapour state. The matter in vapour state can be liquefied by the direct application of than the critical temperature. 
This means the gas has to be converted into vapour first in order to liquefy it by direct application of pressure but without changing its temperature. Gas and vapour are two states of matter in same phenomenon. Intermolecular force of attraction can be neglected in case of gas but it is considered in the case of gas but it is considered in the case of vapor.