What does it mean when a certain axiom is neither provable nor deniable?

What does it mean when a certain axiom is neither provable nor deniable?

What does it mean when a certain axiom is neither provable nor deniable? Does it imply that such axiom is self-evident and can't be doubted? I don't think that "real skeptics"(a skeptic who is so deep in doubt that he doubts his own existence and even his own doubt) like Pyrrho would be happy with that.

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