Volatility Smile depicts the implied volatilities of options with different strikes for the chosen expiration date. Options further out of the money usually have higher implied volatilities, hence the charts show a typical 'smile' shape. The steepness and shape of this smile can be used to assess the relative expensiveness of options, and gauge what kind of tail risks the market is pricing in.

The legend refers to historical overlays and shows the shape of the smile 1 day, 2 days, 1 week, and 2 weeks ago, respectively. For instance, when ATM implied volatility values for extreme strikes is lower today compared to historical overlays could indicate a reduced tail-risk being priced in by the market a probabilities for extreme moves relative to medium moves have come down in the market's view.