A reference of the facts involved in a suit, made by one of the parties, to the oath of the other. It may be made at any stage by either party. The oath, when given, is decisive of the fact referred, and excludes all other proof prior or subsequent. The oath is said to be either affirmative or negative, according as it affirms or denies the fact in question, but sometimes it is qualified, i.e., the party to whom the reference is made does not simply swear yes or no to the question, but adds circumstances relating to it. In this case the Court has to decide whether the circumstances are such as form a necessary part of the oath, or whether they are properly extraneous. In the former case they are called intrinsic, and are received; in the latter case they are called extrinsic, and the oath is read without them.

Source: Kinnear, Digest of House of Lords cases (1865), pg. 360.