never defeated; always victorious

Not deferred.

(programming) Abbreviation of undefined.

Lacking a definition or value. / (mathematics, computing) That does not have a meaning and is thus not assigned an interpretation.

Free from stain, blemish, evil or corruption; immaculate; uncorrupted.

Not defended.

Not definable.

Anything that cannot be defined.

Not defeatable; impossible to defeat.

Something that has an undefeatable quality.