【中文版】

空单是指投资者在股票、期货等交易中卖出开仓的交易单。卖出开仓意味着投资者预测市场价格将会下跌，因此他们通过卖出空单来获取利润。

在股票或期货交易中，投资者可以通过卖出开仓来建立空头头寸。当市场价格下跌时，空头头寸的盈利将会增加，因为投资者是以较低的价格买入，然后以较高的价格卖出。这种交易策略通常被用于短线交易或对市场趋势的短期预测。

然而，空单也存在一定的风险。如果市场价格上涨，空头头寸的投资者将会遭受损失。因此，投资者在选择使用空单时需要谨慎评估市场情况和自身的风险承受能力。

总的来说，空单是股票、期货等交易中的一种重要交易策略，它为投资者提供了获取利润的机会，但同时也存在一定的风险。在使用空单时，投资者需要充分了解市场情况并制定合适的交易计划。

【英文版】

Short position refers to the trading order of investors who sell and open a position in stock or futures trading. Selling and opening a position means that investors predict the market price will fall, so they make profits by selling short.

In stock or futures trading, investors can establish a short position by selling and opening a position. When market prices fall, the profit of the short position will increase, because investors buy at a lower price and sell at a higher price. This trading strategy is usually used for short-term trading or short-term prediction of market trends.

However, there are also risks in short positions. If market prices rise, investors in short positions will suffer losses. Therefore, investors need to carefully evaluate market conditions and their own risk tolerance when choosing to use short positions.

Overall, short positions are an important trading strategy in stock and futures trading, providing investors with opportunities to obtain profits, but there are also certain risks. When using short positions, investors need to fully understand market conditions and develop appropriate trading plans.