A more thorough explanation:

The rule of optional completeness is an evidentiary rule that states when a party presents part of a writing or statement in court, the opposing party can request that the rest of the passage be read to provide the full context.

For example, if a witness testifies about a conversation they had with someone, the opposing party can request that the entire conversation be read out loud to provide a complete understanding of the context.

However, there are limitations to this rule. The remainder of the passage must explain the first part, and it must be relevant to the case. In some jurisdictions, this rule applies to all types of writings, including account books and confessions. But in federal cases, it only applies to writings and recorded statements.

In most jurisdictions, the remainder of the passage is admissible unless it would be unfair or misleading to do so.

Overall, the rule of optional completeness ensures that both parties have access to the full context of any evidence presented in court, allowing for a fair and just trial.