Boiling point of liquids
Liquid and vapour can coexist at many combinations of temperature and pressure. But for most of them they are not in thermodynamic quilibrium.

For a given temperuture, there is only one (vapour partial ) pressure value with both phases in equilibrium.

For a given vapour partial  pressure, there is only one temperature value with both phases in equilibrium. 

This temperature is also the liquid boiling point at the given external ( total ) pressure.

Standard boiling point is then temperature, when vapour partial pressure is equal external pressure 1 atm.

Note that boiling is not state of thermodynamic equilibrium, as there is net change of phase mass and thermal energy.

If partial pressure is higher than the equilibrium pressure for given temperature, the vapour condensates until the pressure reaches the liquid-vapour equilibrium curve of the phase diagram.

If partial pressure is lower than the equilibrium pressure for given temperature, the liquid evaporates until the pressure reaches the liquid-vapour equilibrium curve of the phase diagram.

If total pressure is lower than the vapour pressure for given temperature, the liquid boils until the total pressure reaches the saturated  vapour pressure.