What Is an Auditor's Opinion?
The audit opinion is that part of the auditor's report to the members of an entity in which the auditor expresses an opinion on the extent to which the financial statements are materially misstated.
The fact that it is an opinion, and not a certification, is meant to indicate to financial statement users that the auditor is providing reasonable assurance, and not complete assurance, as to whether or not the financial statements are materially misstated.