An agreement in a criminal case where a prosecutor and a defendant arrange to end the case against the defendant. The defendant agrees to plead guilty (and often allocute) to a more minor offense than charged or to a smaller number of offenses than charged. The prosecutor often agrees to accept a lighter jail sentence or fine. Plea bargains are subject to the approval of the court.
The reasons for plea bargains may be several. In many cases, prosecutors may have brought too serious a charge to fit the facts or available proof. On the other hand, the defendant may be conscious of his own guilt in the matter to a greater or lesser degree, and afraid of receiving too serious a conviction or too harsh a sentence.
In other cases, a defendant may have culpability with others in a criminal matter and at the same time have knowledge which will ensure the success of a broader or more significant prosecution. In such a case, in order to secure the defendant's willingness to testify for the prosecution in other cases, charges or sentencing in his own case may be offered to be lessened if he does, indeed cooperate fully with the prosecution.
In still other cases, prosecutors may be convinced that they have the right defendant and a completely accurate charge as to what crime(s) he committed, and yet the evidence to secure a conviction may be questionable or lacking. It is of benefit to both parties (prosecutor and defendant) to arrange a resolution of the matter without either side taking the chance that the case, once submitted fully to a judge jury, would go completely against them.
Overall, plea bargains serve to ease the caseload of overburdened justice systems, and form a framework wherein the accused and his accusers can reach an agreement which settles the case once and for all, in what is hoped will be a spirit of fairness.