To short a stock, you borrow shares from other investors at your brokerage sort of like how a car loan from your bank is funded from deposits of other bank customers.
You then sell the borrowed shares, pocketing the proceeds. You owe the brokerage a return of the shares, and you’re hoping that down the road the stock price will fall and you can buy shares to return at a lower price. If you shorted at $100 and stock falls to $75, you could then return the shares and make $25 per share in net profit.
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