Definition of Exceptio
An exception, plea, or objection. In civil law, a plea by which the defendant admits the cause of action, but alleges new facts which, provided they be true, totally, or partially answer the allegations put forward on the other side; thus distinguished from a mere traverse of the plaintiff’s averments. In this use, the term corresponds to the common-law plea in confession and avoidance. Such answers to the “defense” or “plea” of the common law. An allegation and defense of a defendant by which the plaintiffs claim or complaint is defeated, either according to strict law or upon grounds of equity. In a stricter sense, the exclusion of an action that lay in strict law, on grounds of equity (actionis jure stricto competentis ob sequitatem exclusio). A kind of limitation of an action, by which it was shown that the action, though otherwise just, did not lie in the particular case. A species of defense allowed in cases where, though the action as brought by the plaintiff was in itself just, yet it was unjust as against the particular party sued.
That's the definition of Exceptio in Black's Law Dictionary 6th Edition. Courtesy of Cekhukum.com.