An exponential function is a mathematical expression in which a constant base is raised to a variable exponent, typically written as $f(x) = a imes b^{x}$, where $a$ is a constant, $b$ is the base, and $x$ is the exponent. This type of function shows rapid growth or decay, depending on whether the base is greater than or less than one, and it plays a vital role in modeling natural phenomena such as population growth and radioactive decay, as well as in solving differential equations.