A short squeeze is a situation in which a stock's price increase triggers a rush of buying activity among short sellers. Short sellers must buy stock to close out their short positions and cut their losses, which results in a further increase in stock prices, which compel still more short sellers to cover their positions.
A short squeeze occurs when the stock's price doesn't decline as anticipated.
Short squeezes occur more often in small-cap stocks with small floats, but they can occur with any stock.