A composite function is formed when one function is applied to the result of another function. If you have two functions, f(x) and g(x), the composite function is written as f(g(x)). This means you first calculate g(x) and then use that result as the input for f(x). Composite functions are useful in various fields, including mathematics and science, as they allow for the combination of different processes or transformations. Understanding how to work with composite functions can help simplify complex problems by breaking them down into manageable steps.