What is Arraignment?

Legal Definition
Arraignment is a formal reading of a criminal charging document in the presence of the defendant to inform the defendant of the charges against him or her. In response to arraignment, the accused is expected to enter a plea. Acceptable pleas vary among jurisdictions, but they generally include "guilty", "not guilty", and the peremptory pleas (or pleas in bar) setting out reasons why a trial cannot proceed. Pleas of "nolo contendere" (no contest) and the "Alford plea" are allowed in some circumstances.
-- Wikipedia
Legal Definition
The first step in criminal proceeding where the defendant is brought in front of the court to hear the charges and enter a plea.
Illustrative caselaw
See, e.g. County of Riverside v. McLaughlin 500 U.S. 44 (1991) and Godinez v. Moran, 509 U.S. 389 (1993).
See also
Legal Definition
Crim. law practice. Signifies the calling of the defendant to the bar of the court, to answer the accusation contained in the indictment. It consists of three parts.

2. – 1. Calling the defendant to the bar by his name, and commanding him to hold up his hand; this is done for the purpose of completely identifying the prisoner, as the person named in the indictment; the holding20up his hand is not, however, indispensable, for if the prisoner should refuse to do so, he may be identified by any admission that he is the person intended. 1 Bl. Rep. 3.

3. – 2. The reading of the indictment to enable him fully to understand, the charge to be produced against him; The mode in which it is read is, after' saying, " A B, hold up your hand," to proceed, "you stand indicted by the name of A B, late of, &c., for that you on, &c." and then go through the whole of the indictment.

4. – 3. After this is concluded, the clerk proceeds to the third part, by adding, " How say you, A B, are you guilty or not guilty?" Upon this, if the prisoner, confesses the charge, the confession is recorded, and nothing further is done till judgment if, on the contrary, he answers "not guilty", that plea is entered for him, and the clerk or attorney general, replies that he is guilty; when an issue is formed. Vide generally, Dalt. J. h. t.; Burn's J. h. t.; Williams; J. h. t.; 4 Bl. Com. 322; Harg. St. Tr. 4 vol. 777, 661; 2 Hale, 219; Cro. C. C. 7; 1 Chit. Cr. Law, 414.
-- Bouviers Law Dictionary
Legal Definition
In criminal practice. Calling the defendant to the bar of the court, to answer the accusation contained in the indictment.
-- Black's Law Dictionary