The notation "f(a)" represents the value of a function f at a specific input a. In mathematics, a function is a rule that assigns each input exactly one output. For example, if f is defined as f(x) = x + 2, then f(3) would equal 5, since 3 + 2 = 5. Functions can be used to model various real-world situations, such as calculating distance based on time and speed. Understanding "f(a)" helps in analyzing how changes in the input affect the output, which is essential in fields like science, engineering, and economics.