Parol Evidence Rule

The parol evidence rule enacts a principle of the common law of contracts that presumes that a written contract embodies the complete agreement between the parties involved; the document is the sole repository of the terms of the contract (Jacobs v. Batavia & General Plantations Trust Ltd [1924] 1 Ch 287). The rule therefore generally forbids the introduction of extrinsic evidence (i.e., evidence of communications between the parties which is not contained in the language of the contract itself) which would add or change terms of a later written contract.
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Noun
1. a rule that oral evidence cannot be used to contradict the terms of a written contract
(hypernym) rule of evidence

Verbal evidence is inadmissible to vary or contradict the terms of a written agreement. - (read more on Parol Evidence Rule)