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

NPS：

A dimensional designation consisting of a combination of letters and numbers used for piping system components, comprising the letters “NPS” followed by a dimensionless integer. This number is directly related to characteristic dimensions such as the bore diameter or outside diameter of the end connection. The dimensionless number may be used as a valve size designation without the “NPS” prefix. The dimensionless number does not represent a measured value and should not be used in calculations.