Personal and Professional Responsibility, page-32

What is public trust?

Public officials are given powers to make decisions or do other things as part of their official roles.

For example, ministers are sometimes given powers under legislation to issue permits or licenses. Other public officials have powers to enter into contracts involving the use of public money, or to grant applications for financial assistance. Each of these powers are granted to the public official ‘on trust’ for the Australian public. That means the power must be exercised for the purposes for which the power was granted, not for some other, improper purpose.

A public official can breach public trust even if they don’t gain any advantage for themselves or someone else. The key element of a breach of public trust is the exercise of an official power other than honestly for the purpose for which it was conferred.

from the above link