Legal Information Institute – Cornell University Law School
Definition:
A rule that governs the extent to which parties to a case may introduce into court evidence of a prior or contemporaneous agreement in order to modify, explain, or supplement the contract at issue. The rule states that where the parties to a contract intended for their written agreement to be the full and final expression of their bargain (i.e., the writing is an integration), other written or oral agreements that were made prior to or simultaneous with the writing are inadmissible for the purpose of changing the terms of the original agreement.
DEFINITION FROM NOLO’S PLAIN-ENGLISH LAW DICTIONARY
If there is a written contract, the terms of the contract cannot be altered by evidence of oral (parol) agreements purporting to change, explain, or contradict the written document.