shorting is identically borrowing. You borrow the stock from someone who owns it, and resell it at the current price. Then later down the road, you buy it back at the lower price and return it to the original owner. You have made money on whatever that difference is. This is not a metaphor, this is how shorting operates.

It can easily go over 100% if the person you sell it to also lends it to someone to short (and they have no clue that the share they bought was involved a short, already).

Note - this is why it's possible to lose your shirt when you are shorting. Eventually you will need to return that stock you've sold, which means buying it at whatever the price is. So if it goes WAAAY up, you lose a lot of money. In contrast to buying a stock, where you can only lose your position.