9F05

Application Discretionary Data is a deliberately open, issuer-defined field with no structure EMV itself specifies - a catch-all the issuer can use for whatever proprietary content doesn't have a dedicated tag of its own, related to the Issuer Application Data (9F10) that plays a similar catch-all role but specifically inside the cryptogram-verification flow rather than as general application data. Because its entire content model is issuer-defined, a generic EMV decoder can report that 9F05 is present and how long it is, but genuinely cannot say more without that issuer's own documentation - unlike almost every other tag in this dictionary, where the format field at least constrains what kind of data to expect, 9F05's format itself is effectively whatever the issuer decided. This makes it one of the more honest fields to document precisely because there's nothing more specific to honestly claim about it: its presence is a signal that an issuer chose to extend the standard rather than a data point with predictable meaning across cards. See EMV 4.4 Book 3.