An offer of proof—also known as an informal bill of exception—is a procedure available during trial for the presentation of evidence the trial court has excluded. An offer of proof is made outside of the jury’s presence and often after the judge has sustained an objection to the admissibility of the evidence.

A bill of exception—also known as a formal bill of exception—is a procedure that allows a party to complain on appeal about evidence that would not otherwise appear in the trial record (because there was no offer of proof made at trial) by detailing the evidence (testimony, etc.) that would have been offered if the trial court had allowed it.

In Maryland, an offer of proof is a procedural mechanism used during a trial when the court excludes evidence. This process allows the attorney to create a record of the evidence that they believe should be admitted. The offer of proof is typically made outside the presence of the jury, following a judge's ruling that sustains an objection to the evidence's admissibility. This is important for preserving the issue for appeal, as it demonstrates to the appellate court what the evidence would have been and allows the court to assess whether excluding it was harmful error. On the other hand, a formal bill of exception is a more antiquated procedure that is not commonly used in modern practice. It was traditionally used to document objections to evidence that was not admitted at trial, without an offer of proof, to ensure that the appellate court could review the decision. However, the modern rules of appellate procedure and evidence have largely replaced the need for formal bills of exception with more streamlined processes for preserving the record for appeal.