Fibonacci numbers refer to a sequence (or ratio) that appears all over.

The first number is 1, then 1, add them together then you get 2. Add the last two numbers, 1 and 2 and you get 3. Add the last two together, you get 5. Add the last two and you get 8. And so on.

0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55...

You will even find these numbers on a piano keyboard. See below: