Audit engagement is normally means the job taken up by an auditor to carry out a statutory audit on the limited company as required under the Companies Ordinance. An engagement letter is usually sent out by the auditor to state out his scope and obligations of him and the client as required by Hong Kong Institute of Certified Public Accountants.
So, in simple term, audit engagement is a job to be carried out by an internal auditor for policies and procedures as defined by the management. It may also means the statutory audit as stated above. The engagement is all bound by the terms of the work and duties of each party.