A challenge.
To challenge (someone) or brave (a hazard or opposition).
to defy an enemy; to defy the power of a magistrate; to defy the arguments of an opponent; to defy public opinion
To refuse to obey.
If you defy your teacher you may end up in detention.
To not conform to or follow a pattern, set of rules or expectations.
To renounce or dissolve all bonds of affiance, faith, or obligation with; to reject, refuse, or renounce.