What does the number "e" represent?

It is an irrational number. the first few digits are:

2.7182818284590452353602874713527

It is known as Euler's number

The actual formula that I have always seen is

e = the limit as n goes to infinity of (1 + 1/n)^n

What that ends up being is

lim n --> infinity of 1 + 1/1 + 1/2! + 1/3! + 1/4^... + 1/n!

e ~ 2.71828

In isn't like pi where that is the ratio of a circle's circumference to the diameter, or anything similar that I am familiar with.

I have included a wikipedia link so you can study more.

It is that number for which the integral of 1/x from 1 to e is 1.

2.718281828

It is used for the Natural Log as well as for Exponential Functions

ofcourse it would be exponent