triple point

the triple point of a substance is the temperature and pressure at which three phases ( gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium. 
Critical point or critical temperature is the temperature after which the gas can not be liquified by application of any amount of pressure.
below critical temperature the phase existing is vapour and above critical temperature the phase is called gas.
From the graph it can be observed that below critical temperature at high pressure liquid phase exists(the right side of the continuous green curve), above critical temperature gas can not be liquified so liquid phase does not exist whatever is the magnitude of pressure.