What is Amnesty?

Legal Definition
Amnesty (from the Greek ἀμνηστία amnestia, "forgetfulness, passing over") is defined as: "A pardon extended by the government to a group or class of persons, usually for a political offense; the act of a sovereign power officially forgiving certain classes of persons who are subject to trial but have not yet been convicted." It includes more than pardon, inasmuch as it obliterates all legal remembrance of the offense. Amnesty is more and more used to express "freedom" and the time when prisoners can go free.

Amnesties, which in the United Kingdom may be granted by the crown or by an act of Parliament, were formerly usual on coronations and similar occasions, but are chiefly exercised towards associations of political criminals, and are sometimes granted absolutely, though more frequently there are certain specified exceptions. Thus, in the case of the earliest recorded amnesty, that of Thrasybulus at Athens, the thirty tyrants and a few others were expressly excluded from its operation; and the amnesty proclaimed on the restoration of Charles II of England did not extend to those who had taken part in the execution of his father. Other famous amnesties include: Napoleon's amnesty of March 13, 1815 from which thirteen eminent persons, including Talleyrand, were exempt; the Prussian amnesty of August 10, 1840; the general amnesty proclaimed by the emperor Franz Josef I of Austria in 1857; the general amnesty granted by President of the United States, Andrew Johnson, after the American Civil War (1861-April 9, 1865), in 1868, and the French amnesty of 1905. Amnesty in U.S. politics in 1872 meant restoring the right to vote and hold office to ex-Confederates, which was achieved by act of Congress. Those were true amnesties, pardoning past violations without changing the laws violated.

The Immigration Reform and Control Act of 1986—signed into law by President Ronald Reagan on November 6, 1986—granted amnesty to about 3 million undocumented immigrants in the United States.
-- Wikipedia
Legal Definition
Under immigration law, amnesty is a governmental pardon for person violating policies related to immigration. Immigration amnesty would include the government forgiving individuals for using false documentation to gain employment in the U.S. and to remain in the country, and would allow illegal immigrants or undocumented aliens to gain permanent residency in the United States.
Legal Definition
Government. An act of oblivion of past offences, granted by the government to those who have been guilty of any neglect or crime, usually upon condition that they return to their duty within a certain period.

2. An amnesty is either express or implied; it is express, when so declared in direct terms; and it is implied, when a treaty of peace is made between contending parties. Vide Vattel, liv. 4, c. 2, 20, 21, 22; Encycl. Amer. h.t.

3. Amnesty and pardon, are very different. The former is an act of the sove reign power, the object of which is to efface and to cause to be forgotten, a crime or misdemeanor; the latter, is an act of the same authority, which exempts the individual on whom it is bestowed from the punishment the law inflicts for the crime he has committed. 7 Pet. 160. Amnesty is the abolition and forgetfulness of the offence; pardon is forgiveness. A pardon is given to one who is certainly guilty, or has been convicted; amnesty, to those who may have been so.

4. Their effects are also different. That of pardon, is the remission of the whole or a part of the punishment awarded by the law; the conviction remaining unaffected when only a partial pardon is granted: an amnesty on the concrary, has the effect of destroying the criminal act, so that it is as if it had not been committed, as far as the public interests are concerned.

5. Their application also differs. Pardon is always given to individuals, and properly only after judgment or conviction: amnesty may be granted either before judgment or afterwards, and it is in general given to whole classes of criminals or supposed criminals, for the purpose of restoring tranquillity in the state. But sometimes amnesties are limited, and certain classes are excluded from their operation.
-- Bouviers Law Dictionary
Legal Definition
A severeign act of pardon and oblivion for past acts, granted by a government to all persons (or to certain persons) who have been guilty of crime or delict, generally political offenses,—treason, sedition, rebellion,—and often conditioned upon their return to obedience and duty within a prescribed time. A declaration of the person or persons who have newly acquired or recovered the sovereign power in a state, by which they pardon all persons who composed, supported, or obeyed the government which has bsen overthrown.

The word "amnesty" properly belongs to international law, and is applied to treaties of peace following a slate' of war, and signifies there the burial in oblivion of the particular cause of strife, so that that shall not be again a cause for war between the parties; and this signification of "amnesty" is fully and poetically expressed in the Indian custom of burying the hatchet. And so amnesty is applied to rebellions which by their magnitude are brought within the rules of international law, and in which multitudes of men are the subjects of the clemency of the government. But in these cases, and in all cases, it means onlv "oblivion," and never expresses or implies a grant. Knote v. United States, 10 Ot. Cl. 407.

"Amnesty" and "pardon" are very different The former is an act of the sovereign power, the object of which is to efface and to cause to be forgotten a crime or misdemeanor; the latter is an act of the same authority, which exempts the individual on whom it is bestowed from the punishment the law inflicts for the crime he has committed. Bouvier; United States v. Bassett, 5 Utah, 131, 13 Pac. 237; Davies v. MeKeeby, 5 Nev. 373 : State v. Blalock, 61 N. C. 247; Knote v. United States, 95 U. S. 149, 152, 24 L. Ed. 442.
-- Black's Law Dictionary
Legal Definition
Governmental condonation. .
-- Ballentine's Law Dictionary