What is Conscience?

Legal Definition
Conscience is an aptitude, faculty, intuition or judgment that assists in distinguishing right from wrong. Moral judgment may derive from values or norms (principles and rules). In psychological terms conscience is often described as leading to feelings of remorse when a human commits actions that go against his/her moral values and to feelings of rectitude or integrity when actions conform to such norms. The extent to which conscience informs moral judgment before an action and whether such moral judgments are or should be based in reason has occasioned debate through much of the history of Western philosophy.

Religious views of conscience usually see it as linked to a morality inherent in all humans, to a beneficent universe and/or to divinity. The diverse ritualistic, mythical, doctrinal, legal, institutional and material features of religion may not necessarily cohere with experiential, emotive, spiritual or contemplative considerations about the origin and operation of conscience. Common secular or scientific views regard the capacity for conscience as probably genetically determined, with its subject probably learned or imprinted (like language) as part of a culture.

Commonly used metaphors for conscience include the "voice within", the "inner light". or even Socrates' reliance on what the Greeks called his "daimōnic sign", an averting (ἀποτρεπτικός apotreptikos) inner voice Socrates heard only when he was about to make a mistake. Conscience, as is detailed in sections below, is a concept in national and international law, is increasingly conceived of as applying to the world as a whole, has motivated numerous notable acts for the public good and been the subject of many prominent examples of literature, music and film.
-- Wikipedia
Legal Definition
The moral sense, or that capacity of our mental constitution, by which we irresistibly feel the difference between right and wrong.

2. The constitution of the United States wisely provides that "no religious test shall ever be required." No man, then, or body of men, have a right to control a man's belief or opinion in religious matters, or to forbid the most perfect freedom of inquiry in relation to them, by force or threats, or by any other motives than arguments or persuasion. Vide Story, Const. 1841-1843.
-- Bouviers Law Dictionary
Legal Definition
The moral sense; the faculty of judging the moral qualities of actions or of discriminating between right and wrong; particularly applied to one's percop-tion and judgment of the moral qualities of his own conduct, but in a wider sense, denoting a similar application of the standards of morality to the acts of others. In law, especially the moral rule which requires probity, justice, and honest dealing between man and man, as when we say that a bargain is "against conscience" or "unconscionable," or that the price paid for property at a forced sale was, so inadequate as to "shock the conscience," This is also the meaning of the term as applied to the jurisdiction and principles of decision of courts of chancery, as in saying that such a court is a "court of conscience," that it proceeds "according to conscience," or that it has cognizance of "matters of conscience." See 3 Bl. Comm. 47-56; People v. Stewart, 7 Cal. 143; Miller v. Miller, 187 Pa. 572, 41 Atl. 277.
See also
-- Black's Law Dictionary
Legal Definition
One’s internal judgment of right and wrong. See 7 Cal. 140.
-- Ballentine's Law Dictionary