What is Petition Of Right?

Legal Definition
In English law, a petition of right was a remedy available to subjects to recover property from the Crown.

Before the Crown Proceedings Act 1947, the British Crown could not be sued in contract. However, as it was seen to be desirable that Crown contractors could obtain redress, lest they be inhibited from taking on such work, the petition of right came to be used in such situations, especially after the Petitions of Right Act 1860 simplified the process. Before the petition could be heard by the courts, it had to be endorsed with the words fiat justitia on the advice of the Home Secretary and Attorney-General. This Latin phrase was normally translated as "Let right be done".

One of the most famous causes célèbres in English law, the Archer-Shee case, arose out of proceedings on a petition of right.

Section 1 of the Crown Proceedings Act 1947 allows claims for which a petition would previously have been demanded to be brought in the courts directly as against any other defendant. However, a petition and fiat still appear to be necessary for personal claims against the monarch.
-- Wikipedia
Legal Definition
Eng. law. When the crown is in possession, or any title is vested in it which is claimed by a subject, as no suit can be brought against the king, the subject is allowed to file in chancery a petition of right to the king.

2. This is in the, nature of an action against a subject, in which the petitioner sets out his right to tbat which is demanded by him, and prays the king to do him right and justice; and, upon a due and lawful trial of the right, to make him restitution. It is called a petition of right, because the king is bound of right to answer it, and let the matter therein contained be determined in a legal way, in like manner as causes between subject and subject. The petition is presented to the king, who subscribes it, with these words, soit droit fait al partie, and thereupon it is delivered to the chancellor to be executed according to law. Coke's Entr. 419, 422 b; Mitf. Eq. Pl. 30, 31; Coop. Eq. Pl. 22, 23.
-- Bouviers Law Dictionary
Legal Definition
In English law. A proceeding in chancery by which a subject may recover property in the possession of the king. See Petition de DROIT.
-- Black's Law Dictionary
Legal Definition
A parliamentary declaration of the liberties of the people, assented to by King Charles I. in 1629. It is to be distinguished from the bili of rights, (1689,) which has passed into a permanent constitutional statute. Brown.
-- Black's Law Dictionary
Legal Definition
A declaration by Parliament of popular liberties under Charles I. See, also, Petition de droit.
-- Ballentine's Law Dictionary