Function notation is a way to represent mathematical functions in a clear and concise manner. It typically uses letters, such as f, g, or h, followed by parentheses containing the input value. For example, f(x) indicates that f is a function of x. This notation helps to easily identify the relationship between the input and output of the function. In function notation, the output is determined by substituting the input value into the function. For instance, if f(x) = 2x + 3, then f(2) would equal 2(2) + 3, which simplifies to 7. This makes it easier to work with functions and understand their behavior.