A liquid at its boiling point is in thermodynamic and phase equilibrium with its coexisting vapor. For a liquid of fixed composition, only one of either pressure or temperature are independent. Thus, one can refer to the boiling temperature or the boiling pressure, in each case implying that the other variable has been specified.
Conventionally, the term boiling point is most frequently used to mean the boiling temperature at a specified pressure. The normal boiling point is the boiling temperature at 1 atmosphere pressure. (See also Boiling.)