Auditing is defined as the on-site verification activity, such as inspection or examination, of a process or quality system, to ensure compliance to requirements. An audit can apply to an entire organization or might be specific to a function, process, or production step. Audit is a “systematic, independent and documented process for obtaining audit evidence [records, statements of fact or other information which are relevant and verifiable] and evaluating it objectively to determine the extent to which the audit criteria [set of policies, procedures or requirements] are fulfilled.” Several audit methods might be employed to achieve the audit purpose.

There are three discrete types of audits: product (which includes services), process, and system. However, other methods, such as a desk or document review audit, might be employed independently or in support of the three general types of audits.Some audits are named according to their purpose or scope. The scope of a department or function audit is a particular department or function. The purpose of a management audit relates to management interests such as assessment of area performance or efficiency.

• An audit may also be classified as internal or external, depending on the interrelationships among participants. Employees of your organization perform internal audits. An outside agent performs external audits. Internal audits are referred to first-party audits, while external audits can be either second      party, or third party.

• Product audit – An examination of a particular product or service (hardware, processed material, software) to evaluate whether it conforms to requirements (that is, specifications, performance standards, and customer requirements).

• Process audit – A verification that processes      are working within established limits. It evaluates an operation or method      against predetermined instructions or standards to measure conformance to its      standards and the effectiveness of the instructions. Such an audit may:

• Check conformance to defined requirements such as time, accuracy, temperature, pressure, composition,responsiveness, amperage, and component mixture.

• Examine the resources (equipment,materials, people) applied to transform the inputs into outputs, the environment, the methods (procedures, instructions) followed, and the measures collected to determine process performance.

• Check the adequacy and effectiveness of the process controls established by procedures, work instructions, flowcharts, and training and process specifications.

• System audit – An audit conducted on a management system. It can be described as a documented activity performed  to verify, by evaluation and examination of objective evidence, that applicable elements of the system are appropriate and effective and have been developed, documented, and implemented in accordance and in conjunction with specified requirements.

• A quality management system audit evaluates an existing quality program to determine its conformance to company policies, contract commitments, and regulatory requirements.

• Similarly, an environmental system audit examines an environmental management system, a food safety system audit examines a food safety management system, and safety system audits and carefully examines the safety management system.