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Key_Vol__Peg_DateKey Peg Date in Vol refers to the date T in the future that defines the time interval over which the stochastic evolution is described by the volatility here.
The exact definition of the time interval depends on the choice Key Vol Spec::Vol Type defined within Vol Spec.
For example, if that choice equals Black, the relevant time interval is the whole period from today until T and the volatility reflects the stochastic evolution during that time.
Another possibility would be a so called "local volatility" type, where the relevant time interval is the infinitesimal period (T, T+dt) and the volatility relates to the stochastic evolution during that infinitesimal period only.