Wiktionary
constant function
n. (context mathematics English) A function whose value is the same for all the elements of its domain
Wikipedia
Constant function
In mathematics, a constant function is a function whose (output) value is the same for every input value. For example, the function y(x) = 4 is a constant function because the value of y(x) is 4 regardless of the input value x (see image).
Usage examples of "constant function".
The rotation affected the axes of hyperspace and altered them, whereby the alteration was a constant function of the speed of rotation.