Domain of definition
of a function
The set on which the function considered is given, that is, the collection $X$ of all elements $x$ with each of which the given function $f$ associates an element $y$ of some set $Y$. Thus, if $f:X \to Y$, then $X$ is called the domain of definition of $f$.
The set of values of $f$, i.e. $f(X)$ if $X$ denotes the domain of definition, is called the range of values of $f$.
Domain of definition. Encyclopedia of Mathematics. URL: http://www.encyclopediaofmath.org/index.php?title=Domain_of_definition&oldid=29271