What does the e on the calculator mean

If a number is too big or too small to fit in a calculater display, often scientific notation using the letter E (or e) for exponent (power or index) will be used

In this case, saseflower, the "e" stands for the irrational number 2.718.......... 

It serves as a base for something called the "natural logarithm"

As you take more science courses in school, you will encounter this number, sooner or later....

You are both right.  

If you see it on the calculator answer then saseflower would be correct. (Although usually it is a capital E)

If you see it on a calc button then it is the irrational number 2.718....  Just like CPhill said