The audit opinion is part of the auditor’s report expressing an opinion on the extent to which the financial statements are materially misstated. The fact that it is an opinion, instead of a certification, is meant to inform financial statement users that the auditor is providing reasonable assurance, rather than a complete assurance, as to whether or not the financial statements are materially misstated.
Where the risk of material misstatement in the audited financial statements is acceptable, the auditor express an unqualified audit opinion on the financial statements; where the risk is not acceptable, the auditor express either a qualified opinion or an adverse opinion. Alternatively, if the auditor failed to collect sufficient information, based on which an audit opinion can be expressed, the auditor may choose not to express an opinion.