Function notation is a way to represent a mathematical function. It is typically written as f(x), where f is the name of the function and x is the input variable. The notation f(x) means "the value of the function f at the input x".

For example, let's say we have a function f(x) = 2x + 3. If we want to find the value of the function when x = 5, we would write f(5) = 2(5) + 3 = 13.

Function notation is useful because it allows us to easily express and manipulate functions in mathematical equations and expressions. It also helps to distinguish between the function itself and the specific input values.