An offer of proof is a kind of motion that a lawyer may present to a judge or to the official presiding over an administrative hearing. It is an explanation made by an attorney to a judge during trial to show why a question which has been objected to as immaterial or irrelevant will lead to evidence of value to proving the case of the lawyer's client. Often the judge will ask: "Where is this line of questions going?" and the offer of proof is the response. The offer provides the opposition a preview of the questions (and helps prevent surprise), but is essential to overcome the objections.
In the context of a trial or a hearing, a presiding judge may issue a ruling denying a party the right to proffer evidence. The party aggrieved by this ruling then has the right to indicate for the record what the evidence would have shown had the adverse ruling not been issued. This is necessary in order to preserve the issue for appeal.
In jury trials, offers of proof may be made outside the hearing of the jury. A party may request a motion in limine (Latin: "at the threshold") made before the start of a trial requesting that the judge rule that certain evidence may, or may not, be introduced to the jury in a trial. In some cases this may be made at the bench (with the court reporter taking down every word spoken by the parties and the judge) or the jury may be excused. It is common for the jury to be excused and for a party to be allowed to continue questioning a witness outside the hearing of the jury until the judge can determine if the evidence sought is relevant and not otherwise excludable.