What is Arrest?

Legal Definition
An arrest is the act of depriving people of their liberty, usually in relation to an investigation or prevention of a crime, and thus detaining the arrested person in a procedure as part of the criminal justice system.

Police and various other bodies have powers of arrest. In some places, the power is more general; for example in England and Wales, any person can arrest "anyone whom he has reasonable grounds for suspecting to be committing, have committed or be guilty of committing an indictable offence," although certain conditions must be met before taking such action.
-- Wikipedia
Legal Definition
An arrest is using legal authority to deprive a person of his or her freedom of movement. An arrest is generally made with an arrest warrant. An arrest may be made without a warrant if reasonable belief of the police officer in the guilt of the suspect, based on the facts and information prior to the arrest. For instance, a warrantless arrest may be legitimate in situations where the police officer has a reasonable belief that the suspect has either committed a crime or is about to commit a crime. The police officer might also arrest the suspect to prevent the suspect’s escape or to preserve the evidence. A warrantless arrest may be invalidated though, if the police officer failed to demonstrate exigent circumstances and probable cause.

The right to make warrantless arrests are commonly defined and limited by statutes subject to the due process guaranty of U.S. Constitution. The suspect arrested without a warrant is entitled prompt judicial determination generally made in 48 hours.

An arrest may trigger certain procedural requirements, such as the person under arrest be given a Miranda Warning.
See also
Legal Definition
In criminal cases. The apprehending or detaining of the person, in order to be forthcoming to answer an alleged or suspected crime. The word arrest is more properly used in civil cases, and apprehension in criminal. A man is arrested under a capias ad respondendum, apprehended under a warrant charging him with a larceny.

2. It will be convenient to consider, 1, who may be arrested; 2, for what crimes; 3, at what time; 4, in what places; 5, by whom and by what authority.

3. – 1. Who may be arrested. Generally all persons properly accused of a crime or misdeameanor, may be arrested; by the laws of the United States, ambassadors (q. v.) and other public ministers are exempt from arrest.

4. – 2. For what offences an arrest may be made. It may be made for treason, felony, breach of the peace, or other misdemeanor.

5. – 3. At what time. An arrest may be made in the night as well as in the day time and for treasons, felonies, and breaches of the peace, on Sunday as well as on other days. It may be made before as well as after indictment found. Wallace's R. 23.

6. – 4. At what places. No place affords protection to offenders against the criminal law; a man may therefore be arrested in his own house, (q. v.) which may be broken into for the purpose of making the arrest.

7. – 5. Who may arrest and by what authority. An offender may be arrested either without a warrant or with a warrant. First, an arrest may be made without a warrant by a private individual or by a peace officer. Private individuals are enjoined by law to arrest an offender when present at the time a felony is committed, or a dangerous wound given – 11 Johns. R. 486 and vide Hawk. B. 1, c, 12, s. 1; c. 13, F3. 7, 8; 4 Bl. Com. 292; 1 Hale, 587; Com. Dig. Imprisonment, H 4; Bac. Ab. Trespass, D.

3. Peace officers may, a fortiori, make an arrest for a crime or misdemeanor committed in their view, without any warrant. 8 Serg. & R. 47. An arrest may therefore be made by a constable, (q. v.) a justice of the peace, (q. v.) slieriff, (q. v.) or coroner. (q. v.) Secondly, an arrest may be made by virtue of a warrant, (q. v.) which is the proper course when the circumstances of the case will permit it. Vide, generally, 1 Chit. Cr. Law, 11 to 71; Russ. on Cr. Index, h. t.
-- Bouviers Law Dictionary
Legal Definition
In criminal practice. The stopping, seizing or apprehending a person by lawful authority; the act of laying hands upon a person for the purpose of taking his body into custody of the law; the restraining of the liberty of a man's person in order to compel obedience to the order of a court of justice or to prevent the commission of a crime or to insure that a person charged or suspected of a crime may be forthcoming to answer it French v. Bancroft, 1 Mete. (Mass.) 502; Emery v. Chesley, 18 N. H. 201; In S. v. Benner, 24 Fed. Cas. 1084; Rhodes v. Walsh, 55 Minn. 542, 57 N. W. 212, 23 In R. A. 632; Ex parte Sherwood, 29 Tex. App. 334, 15 S. W. 812. Arrest is well described in the old books as "the beginning of imprisonment, when a man is first taken and restrained of his liberty, by power of a lawful warrant." 2 Shep. Abr. 299; Wood, Inst Co.m. Law, 575. In civil practice. The apprehension of a person by virtue of a lawful authority to answer the deinand against him In a civil action. In admiralty practice. In admiralty actions a ship or cargo is arrested when the marshal has served the writ in an action in rem. Williams & B. Adm. Jur. 193; Pelham v. Rose, 9 Wall. 103, 19 L. Ed. 602. Synonyms distinguished. The term "apprehension" seems to be more peculiarly appropriate to seizure on criminal process; while "arrest" may apply to either a civil or criminal action, but is perhaps better confined to the former. Montgomery County v. Robinson. 85 III. 176. As ordinarily used, the terms "arrest" and "attachment" coincide in meaning to some extent, though in strictness, as a distinction, an arrest may be said to be the act resulting from the service of an attachment; and, in the more extended sense which is sometimes given to attachment, including the act of taking, it would seem to differ from arrest, in that it is more peculiarly applicable to a taking of property, while arrest is more commonly used in speaking of persons. Bouvier. By arrest is to be understood to take the party into custody. To commit is the separate and distinct act of carrying the party to prison, after having taken him into custody by force of the execution. French v. Bancroft, 1 Mete. (Mass.) 502.
See also
-- Black's Law Dictionary
Legal Definition
To take one into custody, to confine him or to restrain his liberty by physical force or threats thereof; to take one into the custody of the law. See 107 Am. St. Rep. 745.
-- Ballentine's Law Dictionary
Legal Definition
To stop; to seize; to deprive one of his liberty by virtue of legal authority.
-- Bouviers Law Dictionary