Essentially there was a hedge fund who was heavily short in GameStop stock to the tunes of many millions. Once the subreddit community of WallStreetBets started applying buy pressure it made the shorts either add more/cover; or have to sell and when they do it adds buy pressure to the book. Led to a big gamma squeeze and this fund got caught off guard with poor risk management and the stock surged so much letting the small joe win for once in a game of smoke screen tactics by larger funds