Short squeeze

In finance, a short squeeze is a rapid increase in the price of a stock that occurs when there is a lack of supply and an excess of demand for the stock.Short squeezes result when short sellers cover their positions on a stock. This can occur if the price has risen to a point where these people simply decide to cut their losses and get out. (This may happen in an automated manner if the short sellers had previously placed stop-loss orders with their brokers to prepare for this eventuality.) Since covering their positions involves buying shares, the short squeeze causes an ever further rise in the stock's price, which in turn may trigger additional covering.
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A situation in which a lack of supply tends to force prices upward. In particular, a situation when prices of a stock or commodity futures contracts start to move up sharply and many traders with short positions are forced to buy stocks or commodities in order to cover their positions and prevent (limit) losses. This sudden surge of buying leads to even higher prices, further aggravating the losses of short sellers  who have not covered their positions.