Euler's number, often written as e, is a special number that helps us understand a lot of math. It's a number like any other, but it's really important because it's a part of many formulas or equations. It helps us understand how things like circles, boxes, and lots of different shapes change as we make them bigger or smaller. This number is actually not a real number—it's what we call an "imaginary number," which means it can't be written as a regular number. That's why we use e instead. It's about 2.718281828459, but it keeps going forever!