The "Entire Agreement" or "Integration" clause defines what is and is not a part of the agreement. It codifies the parol evidence rule, which simply stated provides that "the final agreement made by the parties supercedes any terms discussed in earlier negotiations."
What Is The Parol Evidence Rule?, New Jersey Law Blog (November 9, 2006)
Entire Agreement. This Agreement (together with the documents [referred to in this Agreement] [listed on Exhibit A]) constitute(s) the entire agreement between the parties with respect to its subject matter and constitutes and supersedes all prior agreements, representations and understandings of the parties, written or oral.
Larger Scope - Transaction Documents, not Agreement
Entire Agreement. The Transaction Documents, together with the exhibits and schedules thereto, contain the entire understanding of the parties with respect to the subject matter hereof and supersede all prior agreements and understandings, oral or written, with respect to such matters, which the parties acknowledge have been merged into such documents, exhibits and schedules.
Agreement Supersedes Trade Language
Entire Agreement. This Agreement, together with the exhibits and schedules hereto, constitutes the entire understanding and agreement of the parties hereto with respect to the subject matter hereof and supersedes all prior and contemporaneous agreements or understandings, inducements or conditions, express or implied, written or oral, between the parties with respect hereto other than the Confidentiality Agreement. The express terms hereof control and supersede any course of performance or usage of the trade inconsistent with any of the terms hereof.
Peter Linzer writes that "the parol evidence rule fits none of the words in its name: it is not limited to parol--that is, oral--testimony, it is not evidentiary, and is not really a rule.
The Comfort of Certainty: Plain Meaning and the Parol Evidence Rule, 71 Fordham L. Rev. 799 (2002-2003).
The challenge for contract drafting is that language is never perfectly clear and unambiguous. Frequently, it must be "interpreted", sometimes beyond the four corners of the document, creating a continuum from strict interpretation (Williston) to more liberal guides (Corbin, The Restatement of Contracts Second, ). For example, UCC § 2‐202 provides exceptions for course of dealing or custom: