A short squeeze occurs when a stock or other asset jumps sharply higher, forcing traders who had bet that its price would fall, to buy it in order to forestall even greater losses. Their scramble to buy only adds to the upward pressure on the stock's price. Short-sellers borrow shares of an asset that they believe will drop in price in order to buy them after they fall.
If they're right, they return the shares and pocket the difference between the price when they initiated the short and the actual sale price. If they're wrong, they're forced to buy at a higher price and pay the difference between the price they set and its sale price. Short sales have an expiration date, so when a stock unexpectedly rises in price, the short-sellers may have to act fast to limit their losses.
So basically what's happening right now is that there is a reddit forum https://www.reddit.com/r/wallstreetbets/... that's trying to fight against institutional investors like hedge funds because they have been earning money off investors by shorting more than 100% for the available stocks which technically should not be possible. That said, this stock has not much fundamental value is definitely overvalued right now but its more of a movement to fight against the rich rather than just simply investing itself.