The boiling point is defined as the temperature at which a liquid changes into vapor under specific atmospheric pressure conditions.
This is the process by which molecules in a liquid state (e.g. water) spontaneously become gaseous state (e.g. steam), usually under the influence of heat.
The pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases at a given temperature in a closed system.
This is the change of the physical state of matter from gas phase into liquid phase, and is the reverse of evaporation.