The definition of a set by enumerating its members. An extensional definition can always be reduced to an intentional one.
An extension field is sometimes also called simply an extension.
Set Extension
See also
Extension Field, IntensionExplore with Wolfram|Alpha
References
Russell, B. "Definition of Number." Introduction to Mathematical Philosophy. New York: Simon and Schuster, 1971.Referenced on Wolfram|Alpha
Set ExtensionCite this as:
Weisstein, Eric W. "Set Extension." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/SetExtension.html