smile
 n.— «A reference to the common shape of a graph of at- or out-of-the-money put and call implied volatilities for options with a common expiration date. The name comes from the fact that the furthest out of the money options generally have the highest implied volatilities, causing the ends of the graph to turn up. » —by Gary L. Gastineau, Mark P. Kritzman Dictionary of Financial Risk Management , 1999. (source: Double-Tongued Dictionary)