The main objective of audit is that it checks the compliance with planned arrangement and implementation.
It is one type of an information gathering activity by the auditors for making improvement and corrective action.
The audit which is performed may be Internal or External and do not necessarily have to cover the whole system at once but it may cover some of the elements of the system.
The first party audit is an audit carried out by an organization itself which is known as Internal Audit.
A second party audit by one organization , working on its own behalf , on another i.e, audit on supplier by a customer
Third party is an audit by independent organization on supplier.