A short squeeze is a phenomenon where a stock's price spikes sharply, rapidly and extensively, forcing short sellers to buy shares to cover their positions to avoid more significant losses. As share prices rise, the value of their short position may rise beyond the margin limits. This can trigger a margin call, which requires the trader to deposit more capital into the account or buy back shares to cover some or all of the short positions and take the losses. All short selling is done with a margin account. You can only borrow shares in a margin account.
If a stock squeezes high enough, like squeezing up over 100% in an hour, it can trigger a forced liquidation, a margin call that automatically covers the short position at market prices. This means the broker will automatically repurchase the shares using market orders to cut the losses in the account. Market buy orders can result in expensive buy covers during a short squeeze. Forced liquidations can happen automatically without warning. For this reason, it's very critical to be aware of the maintenance margin requirements on any stock you are short. Brokers can adjust the maintenance margin abruptly during the day, so stay on top.