Plea

n. (Law) request, appeal; excuse, pretext; statement, affidavit; defendant's answer to a charge

In legal terminology, a plea is simply an answer to a claim made by someone in a civil or criminal case under common law using the adversary system. Colloquially, a plea has come to mean the assertion by a criminal defendant, at arraignment or otherwise in response to a criminal charge, whether he is guilty or not guilty.
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Noun
1. a humble request for help from someone in authority
(synonym) supplication
(hypernym) entreaty, prayer, appeal
2. (law) a defendant's answer by a factual matter (as distinguished from a demurrer)
(hypernym) answer
(hyponym) counterplea
(classification) law, jurisprudence
3. an answer indicating why a suit should be dismissed
(hypernym) due process, due process of law
(part-holonym) trial
(classification) law, jurisprudence

(n.)
That which is alleged or pleaded, in defense or in justification; an excuse; an apology.
  

(n.)
That which is alleged by a party in support of his cause; in a stricter sense, an allegation of fact in a cause, as distinguished from a demurrer; in a still more limited sense, and in modern practice, the defendant's answer to the plaintiff's declaration and demand. That which the plaintiff alleges in his declaration is answered and repelled or justified by the defendant's plea. In chancery practice, a plea is a special answer showing or relying upon one or more things as a cause why the suit should be either dismissed, delayed, or barred. In criminal practice, the plea is the defendant's formal answer to the indictment or information presented against him.
  

(n.)
An urgent prayer or entreaty.
  

(n.)
A cause in court; a lawsuit; as, the Court of Common Pleas. See under Common.
  

A defendant's reply to a charge put to him by a court; ie guilty or not guilty