Verifiable evidence is information that can substantiate that a security control has been implemented and exists or operates as intended. Examples include access-review records, configuration histories, test results, incident logs, and approvals. Useful evidence is traceable to a specific control, sufficiently current, and available for review.
It matters because policies describe expectations, while evidence helps show what happens in practice. In security assurance and compliance, organizations may use evidence to assess control effectiveness, identify gaps, and demonstrate oversight. Evidence should be collected and maintained through repeatable processes, with clear ownership and appropriate protection against alteration or unauthorized access. A document alone is not proof that a control is working; validation may require operational records or testing.