# C# Programming/Keywords/double

The double keyword is used in field, method, property, and variable declarations and in cast and typeof operations as an alias for the .NET Framework structure System.Double. That is, it represents an IEEE 754, 64-bit signed binary floating point number whose value is negative 0, positive 0, negative infinity, positive infinity, not a number, or a number ranging either from ${\displaystyle -5.0\times 10^{-324}}$ to ${\displaystyle -1.79\times 10^{308}}$ or from ${\displaystyle 5.0\times 10^{-324}}$ to ${\displaystyle 1.79\times 10^{308}}$.