An audit log records significant events, such as sign-ins, permission changes, document access, approvals, releases, and data exports, along with the user, time, and affected record. It lets an organization reconstruct what happened and prove that controls were followed.
To be trustworthy, audit logs must be protected from tampering. Ideally the application cannot edit or delete them, access is restricted, and they are retained according to policy. Logs are most useful when they are reviewed, not just collected.