# What is base e?

Any number greater than 0 (except for 1) can be used for an exponential function. "e", called "Euler's Constant" (pronounced oiler) is one of the most commonly used bases, i.e. $y = {e}^{x}$.
It occurs in many applications such as statistics and finance. "e" can be defined as follows. If you take the function $y = {\left(1 + \frac{1}{x}\right)}^{x}$ and then allow x to get larger and larger (approaching infinity), then y will approach the constant e, which is approximately 2.718.