GameStop is a struggling retail company that sells video games, equipment, and accessories.

Many people have been predicting, for years now, that the company's finances would continue to get worse and worse, and eventually go into bankruptcy.

In the stock market, there's a tool called a "short". If you think that a stock is going to lose money, you can do the following: 1) Borrow shares from someone that owns them, with the promise to return the same number of shares later 2) Sell those shares at today's prices 3) When the loan comes due, buy shares of that stock at the new price, and give them back to the person you borrowed from.

If the stock is worth less at step 3 than at step 2, you've made money (you borrow a share when it's at $100, sell it for $100, and then buy it back later for $50. The loaner gets their share back and you keep the extra $50).

However, if the stock is worth more at step 3 than at step 2, you've lost money, because you still need to return the share that you borrowed, which means you need to buy it back at the now higher price.

What happened with GameStop was that a lot of hedge funds - investors managing millions or billions of dollars in other people's money - bet that GameStop would do poorly and so short the stock.

People on /r/WallStreetBets realized that there were more shares being borrowed than there were shares that actually existed, which meant that if the price were to increase, the people that owned the shares would make a lot of money and the people that shorted the shares would lose a lot of money.

So they bought as many shares as they could, which rose the price, which caused short sellers to panic, which got publicity. That caused more people to buy in, which made the hedge funds' positions even worse.