a2 Sales Update on Alibaba, page-57

A stock with very high short interest may occasionally surge in price—typically when a positive development in the stock or broad market triggers massive short-covering—creating what is known as a “short squeeze”. Heavily shorted stocks are also vulnerable to “buy-ins”, which occurs when a broker-dealer closes out short positions in a difficult-to-borrow stock because its lenders are demanding it back. The risk of a “buy-in” is a major risk with short selling because of its unpredictability and can lead to unexpected losses for the short seller.