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 can be useful in various fields, such as mathematics and computer science, as they allow for more complex operations to be simplified. Understanding how to combine functions helps in solving equations and modeling real-world scenarios effectively.