An auditor is a public officer charged by law with the duty of auditing and verifying the expenditure of public funds, or an accountant who performs a similar function for private companies.
An audit is an unbiased examination and evaluation of the financial statements of an organization, typically performed by an outside accountant or accounting firm. The term "audit" also means an examination of a taxpayer's return or other transactions by the federal taxing authority.
In Canada, the United States and the UK, there are exemptions that exempt many private limited companies from having to have their annual financial statements audited. However, if the number of shareholders exceeds a certain number or if the company's revenues are above a certain threshold, the company may be required to produce audited financials. If the shares are traded publicly, an audit is required.