It stands for non-audit service; a service (that can or cannot be offered by an accounting/ audit firm) other than annual financial statements audit, including assurance, tax, advisory and other services that do not relate to core audit services. It also includes various services such as risk assessment, performance measurement, management advisory, accounting and review, executive recruitment, legal help and corporate recovery, assurance on an entity’s information system, attestation services for certifying the soundness of internal control systems, financial forecasts, and projections, among others.

Prohibited non-audit services (also known as blacklist non-audit services) are those an auditor/ audit firm cannot provide to an auditee (an audited firm). Allowed non-audit services (also called whitelist non-audit services) are those that can be provided by an auditor, including assurance services, as specific measures are usually taken by regulatory authorities to constrain independence issues (by placing a cap on allowed services).

NAS may also denote non-assurance services.