What is e (2.718…) and why does it literally appear everywhere?

Question

What is e (2.718…) and why does it literally appear everywhere?

In: 756

Answer 1

other people gave an interesting definition and it’s used. Another interesting fact not mentionned :e=1 + 1/1 + 1/1*2 + 1/1*2*3 + 1/1*2*3*4 + … + 1/n!