There are 4 possible types of audit opinions that the auditor can provide for an audit.
Unqualified Opinion: The unqualified opinion means that the report is ‘clean’ and the auditor did not find any issues that could impact the conclusion that the audit objectives were met. Think of the word unqualified to mean that there is no asterisk to the opinion and that the auditor is confident that the audit objectives were met. In other words, the audit had no issues that will impact the qualification of the auditor opinion. Please note that it does not mean there were no control failures at all. It just means that the aggregate of the failures was not significant to impact the opinion of the audit.
Qualified Opinion: The qualified opinion means that the report is not ‘clean’ and the auditor’s opinion has an asterisk due to certain significant issues that were identified in the report. So, the auditor is not able to fully state that the audit objectives were met due to some significant issues/deficiencies that were noted during the audit. Typically, the issues will also be described as part of the opinion.
Adverse Opinion: This is essentially a negative opinion due to significant and material issues that the auditor identified. Typically, this means that clients cannot rely on the systems of the entity being audited.
Disclaimer: This opinion means that the auditors cannot provide an opinion on the audit due to insufficient information. The nature of the insufficient information may or may not mean there are significant issues with the environment. So, this kind of report is not useful to clients because they can’t tell if the audit would have passed or failed.