之所以被称为“波动率微笑”，是指价外期权和价内期权（out of money和 in the money）的波动率高于平价期权（at the money）的波动率，使得波动率曲线呈现出中间低两边高的向上的半月形，像是微笑的嘴形。
The Black-Scholes model predicts that the implied volatility curve is flat when plotted against varying strike prices. Based on the model, it would be expected that the implied volatility would be the same for all options expiring on the same date with the same underlying asset regardless of the strike price. Yet, in the real-world, this is not the case.
Black-Scholes模型预测，执行价格相变动时，蕴含波动率曲线是平坦的。根据该模型，无论执行价格如何，在同一标的资产到期日到期的所有期权的隐含波动率都是相同的。然而，在现实世界中，情况并非如此。
When options with the same expiration date and the same underlying asset, but different strike prices, are graphed for implied volatility the tendency is for that graph to show a smile.The smile shows that the options that are furthest in- or out-of-the-money have the highest implied volatility.当相同到期日、相同标的资产、但执行价格不同的期权被绘制成隐含波动率曲线图时，该线图的形状像微笑。微笑曲线表明，价外或价内期权的隐含波动率最高。
（金融+会计+商务）英语核心词汇：
volatility smile 波动率微笑
隐含波动率 implied volatility
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