A formal petition is a written request to a government or other official body, usually signed by many people, asking for some kind of action. The term 'formal petition' can also refer to a legal document that is filed with a court to start a legal action. The crossword solution for the term 'formal petition' is 'PLEA'. A PLEA is a formal request made to a court or other authority, typically as part of a legal process. It is usually made by a defendant in a criminal case, asking for leniency or mercy.