Is an irrational number just a way to describe a number that's lost its mind? Not really. :) An irrational number is simply a number that cannot be written as a fraction. Check out the definition, learn an important property of these special numbers, and take a look at some examples of irrational numbers.
In math, 'e' isn't just a letter, it's an irrational number! This tutorial shows you how mathematicians use the letter 'e' to represent a specific value and how having a base of 'e' is called a natural base.