What is the nominal pipe size (NPS) of a valve?

NPS：

Combined alphanumeric size designation for piping system components consisting of the letters NPS followed by a dimensionless integer number. This number is directly related to a characteristic dimension such as the bore or outside diameter of the end connection. The dimensionless number may be used as a dimensional designation for valves without the prefix “NPS”. Dimensionless size numbers do not represent measured values and cannot be used for calculations.