A situation where the implied volatility (volatility skew) remains unchanged (i.e., it sticks) for any given moneyness. In other words, the implied volatility of an option , for a particular maturity, is assumed to be dependent on the underlying price (spot price: S) and the option’s strike price (K). The moneyness variable (K/ S) is a basic measure of moneyness (a more practical measure is K/ F, where F is the forward value of spot price, S).

It is also known as a sticky delta or volatility by delta.