well-defined function
nounUK /ˌwel dɪˈfaɪnd ˈfʌŋkʃən/
US /ˌwel dɪˈfaɪnd ˈfʌŋkʃən/
A well-defined function is a rule that gives exactly one answer for each input.
The teacher said our rule was a well-defined function because every number we put in got only one answer out.
OTHER MEANINGS
2. In programming, a function whose result depends only on its inputs and is always the same for the same inputs.
Our sorting routine is a well-defined function, so it returns the same list order every time.
3. A function that is clearly and precisely specified, leaving no room for confusion about what it does.
The manual gives a well-defined function for each button on the machine.
4. A mathematical function that assigns exactly one output to every element of its domain.
The formula f(x) = x + 1 is a well-defined function on the real numbers.