Generally, allocute means "to speak out formally." In the field of apologetics, allocution is generally done in defense of a belief. In politics one may allocute before a legislative body in an effort to influence their position on an issue. In law, it is generally meant to state specifically and in detail what one did and/or why, often in relation to commission of a crime.
In most jurisdictions, a defendant is allowed the opportunity to allocute - that is, explain himself, before sentence is passed. Some jurisdictions hold this as an abolute right, and in its absence, a sentence may potentially be overturned, with the result that a new sentencing hearing must be held.
Allocution is sometimes required of a defendant who pleads guilty to a crime in a plea bargain in exchange for a reduced sentence. In this instance, allocution can serve to provide closure for victims or their families. In principle, it removes any doubt as to the exact nature of the defendant's guilt in the matter. However, there have been many cases in which the defendant allocuted to a crime that he did not commit, often because this is a requirement to receiving a lesser sentence.
see confession