An audit is a process in which an independent auditor examines the functioning of a given area. It obtains irrefutable evidence of how the area works and reveals discrepancies that hinder the achievement of the area's goals or other mission. You may meet with auditors in the areas of finance, processes, management, lean manufacturing, 5S, information security (cyber security), communications, marketing, etc. There is a big difference between external audit and internal audit. Internal auditors should rather help "their colleagues", than just pointing out the errors in the form of findings or discrepancies.