Most often, the term warrant refers to a specific type of authorization; a writ issued by a competent officer, usually a judge or magistrate, which commands an otherwise illegal act that would violate individual rights and affords the person executing the writ protection from damages if the act is performed.
Warrants are typically issued by courts and are directed to the sheriff, constable or a police officer. The warrants issued by a court normally are search warrants, arrest warrants, and execution warrants. A typical arrest warrant in the United States will take the approximate form of:
"This Court orders the Sheriff or Constable to find the named person, wherever he may be found, and deliver said person to the custody of the Court."
Warrants are also issued by other government entities, particularly legislatures, since most have the power to compel the attendance of their members. This is called a call of the house.