Public Policy is equivalent to the Policy of Law. Therefore any acts that have a mischievous tendency so as to be injurious to the interest of the state or the public is stated to be against Public Policy.
An agreement under the Indian Contract Act is unlawful if the court regards it as opposed to public policy
Explaining the scope of the expression public policy and the role of the judges the High Court observed that - the twin touchstone of public policy are, advancement of the public good and prevention of public mischief and these questions have to be decided by the judges not as men of legal learning but as experienced and enlightened members of the community representing the highest common factor of public sentiment and intelligence. (Gherulal V Mahadeodas Maiya)
You may also give these articles a read which have covered public policy in detail. Here is the link:
Hope this helps you.