Pleading
Pleading is usually the first step in a lawsuit. This is when parties formally submit their claims and defenses. A complaint is the first pleading filed by a plaintiff which starts the lawsuit. A complaint lists the  relevant allegations of fact which leads to one or more legal causes of action. It also has a prayer for relief and sometimes a statement of damages claimed. This is called an ad quod damnum clause.  In some situations, a complaint is called a petition. In this case the party filing a complaint is called the petitioner and the other party is the respondent.  In equity, sometimes called chancery, the initial pleading may be called either a petition or a bill of complaint in chancery.