e Is a mathematical constant that is the base of the natural logarithm. The first reference to e was published in 1618 but it did not contain the constant itself.The discovery of e itself is credited to Jacob Bernoulli. The applications used for this constant are mainly in compound interest.
sources:http://www-history.mcs.st-and.ac.uk/HistTopics/e.html, https://en.wikipedia.org/wiki/E_(mathematical_constant)