These days, when you see a sharp rise in the stock market, you can't necessarily attribute it to the bullishness of investors. There's a good chance it's due to short-covering or a short squeeze.A short squeeze takes place when short-sellers quickly cover their bearish positions on optimistic news, which can move the price of the stock up sharply. The metric for measuring short-squeeze opportunities is the short ratio, also known as the "days-to-cover ratio," which is the number of days it would take the short-sellers to cover their positions based on recent average daily volume of the stock. Stockpickr has reviewed the heavily shorted New York Stock Exchange stocks and developed a list of the top NYSE short-squeeze plays for the month of December. To read more, visit Stockpickr.com.