In United States law, a motion is a procedural device to bring a limited, contested issue before a court for decision. It is a request to the judge (or judges) to make a decision about the case. Motions may be made at any point in administrative, criminal or civil proceedings, although that right is regulated by court rules which vary from place to place. The party requesting the motion may be called the moving party, or may simply be the movant. The party opposing the motion is the nonmoving party or nonmovant.
In the United States, as a general rule, courts do not have self-executing powers. In other words, in order for the court to rule on a contested issue in a case before it, one of the parties or a third party must raise an appropriate motion asking for a particular order. Some motions may be made in the form of an oral request in open court, which is then either summarily granted or denied orally by the court. This is still common with motions made during trial.
Today, however, most motions (especially on important or dispositive issues that could decide the entire case) are decided after oral argument preceded by the filing and service of legal papers. That is, the movant is usually required to serve advance written notice along with a written legal argument and a supporting factual foundation to explain why the movant is entitled to the relief requested. The legal argument usually comes in the form of a memorandum of points and authorities, while the evidence of the facts supporting the legal argument is normally supplied in the form of affidavits or declarations under penalty of perjury (which may in turn authenticate attached documentary exhibits).
A few U.S. states have a tradition in which the legal argument comes in the form of an affidavit from the attorney, speaking personally as himself on behalf of their client. In contrast, in most U.S. states, the memorandum is written impersonally, or as if the client were speaking directly to the court, and the attorney reserves declarations of their own personal knowledge to a separate affidavit or declaration (which are then cited to in the memorandum).