Retail investors are banding together to cause price breakouts of shorted stocks. Retail investors, what Wall Street calls the dumb money have piled into stocks that have a large amount of outstanding shorts, or short positions, which is a hedge or bet that the stock will go down. In the case of GameStop at least two hedge funds have had to liquidate their short positions Melvin Financial and Citron. The experienced margin calls. The short squeeze is when those on the short position are forced to liquidate due to the stock going up, it can become a feedback loop.