What is the meaning of Monotone_function?

A function f : XR (where X is a subset of R, possibly a discrete set) that either never decreases or never increases as its independent variable increases; that is, either xy implies f(x) ≤ f(y) or xy implies f(y) ≤ f(x).

A function f : XY (where X and Y are posets with partial order "≤") with either: (1) the property that xy implies f(x) ≤ f(y), or (2) the property that xy implies f(y) ≤ f(x).

A Boolean function with the property that switching any one input variable from 0 to 1 results either in no change in output or a change from 0 to 1.

Source: wiktionary.org