A more thorough explanation:

Definition: Complete Integration refers to a record of the full expression of two parties’ intent. It means that an oral discussion or written document captures the entire agreement between the parties on a particular subject matter. This is different from partial integration, which only expresses some of the terms of an agreement.

For example, if two parties sign a contract that outlines all the terms of their agreement, including the price, delivery date, and quality of goods, then that contract is a complete integration. However, if they only agree on the price and delivery date, but not the quality of goods, then that contract is a partial integration.

Whether integration exists is often a point of dispute in contract law. Contract disputes often involve what exactly was agreed upon between two parties in a given contract. If the contract in dispute is completely integrated, then evidence outside the terms of the contract, such as oral agreements or evidence of past contracts, is inadmissible to contradict the terms of that contract.

For instance, if two parties sign a contract that includes an integration clause, which states that the written contract is the complete and final agreement between the parties, then neither party can introduce evidence of any prior oral agreements or negotiations that contradict the terms of the written contract.

Establishing that a contract is completely integrated can prevent another party from raising contradictory oral agreements or evidence of past contracts. To establish that a given contract is completely integrated, that contract will often contain an integration clause.