"An arrest warrant is an official document, signed by a judge (or magistrate), authorizing a police officer to arrest the person or persons named in the warrant. Warrants typically identify the crime for which an arrest has been authorized, and may restrict the manner in which an arrest be made.
Finally, some warrants also specify the bail that a defendant must post to regain freedom following arrest. If the warrant is for a previous failure of the suspect to appear in court- called a bench warrant- it will probably specify that the arrested person may not be released at all (sometimes termed a "no-bail warrant." -From, "The Criminal Law Handbook"