A petition is a request to do something, most commonly addressed to a government official or public entity. Petitions to a deity are a form of prayer called supplication.
In the colloquial sense, a petition is a document addressed to some official and signed by numerous individuals. A petition may be oral rather than written, or may be transmitted via the Internet.
Petition can also be the title of a legal pleading that initiates a legal case. The initial pleading in a civil lawsuit that seeks only money (damages) might be called (in most U.S. courts) a complaint. An initial pleading in a lawsuit that seeks non-monetary or "equitable" relief, such as a request for a writ of mandamus or habeas corpus, custody of a child, or probate of a will, is instead called a petition.
Act on petition is a "summary process" used in probate, ecclesiastical and divorce cases, designed to handle matters which are too complex for simple motion. The parties in a case exchange pleadings until a cause for a hearing is settled.Black's Law Dictionary specifies it as an obsolete method used in admiralty cases. In the United States, the "act on petition" has been used in maritime cases.
In pre-modern Imperial China petitions were always sent to an Office of Transmission (Tongzheng si or 通政司) where court secretaries read petitions aloud to the emperor. Petitions could be sent by anybody, from a scholar-official to a common farmer, although the petitions were more likely read to the emperor if they were persuasive enough to impeach questionable and corrupt local officials from office. When petitions arrived to the throne, multiple copies were made of the original and stored with the Office of Supervising Secretaries before the original written petition was sent to the emperor.