This is a very good explainer on GameStop’s stock roller coaster this week

(arstechnica.com)

To understand what's happening to GameStop stock, first you have to understand short selling, where investors make a bet that a stock will go down instead of up. To do this, they borrow a share of the stock (for a fee), immediately sell it to pocket the current value, and agree to buy another share later to "cover" their short position.

But shorting stocks comes with huge risks if the stock price goes up. When your short position eventually comes due, you're forced to buy the stock at whatever price the market currently sets, and there's theoretically no limit to how high it could go. If you invest $1,000 in buying a stock, all you can lose is $1,000. If you borrow $1,000 worth of stock to short it, you could lose a lot more than that when you're forced to buy much more expensive stock.

A good explainer on how GameStop exploded the market this week.