ATM Def
Key ATM Def in Fx Vol Spec refers to a choice from the list ATM Def
The entry here supplies the ATM (At-The-Money) definition that applies on the ATM vol quotes specified in the column #ATM of the table supplied through the key Vol Set, but only if their associated option expiry T satisfies T < Tˢʷⁱᵗᶜʰ, where the switch time Tˢʷⁱᵗᶜʰ is specified through the key Switch Tenor or Switch Date