Policy
A policy is a deliberate system of principles to guide decisions and achieve rational outcomes. A policy is a statement of intent, and is implemented as a procedure or protocol. Policies are generally adopted by a governance body within an organization. Policies can assist in both subjective and objective decision making. Policies to assist in subjective decision making usually assist senior management with decisions that must be based on the relative merits of a number of factors, and as a result are often hard to test objectively, e.g. work-life balance policy. In contrast policies to assist in objective decision making are usually operational in nature and can be objectively tested, e.g. password policy.
Public
In public relations and communication science, publics are groups of individual people, and the public (a.k.a. the general public) is the totality of such groupings. This is a different concept to the sociological concept of the Öffentlichkeit or public sphere. The concept of a public has also been defined in political science, psychology, marketing, and advertising. In public relations and communication science, it is one of the more ambiguous concepts in the field. Although it has definitions in the theory of the field that have been formulated from the early 20th century onwards, it has suffered in more recent years from being blurred, as a result of conflation of the idea of a public with the notions of audience, market segment, community, constituency, and stakeholder.
Public Administration
Public Administration is the implementation of government policy and also an academic discipline that studies this implementation and prepares civil servants for working in the public service. As a "field of inquiry with a diverse scope" whose fundamental goal is to "advance management and policies so that government can function". Some of the various definitions which have been offered for the term are: "the management of public programs"; the "translation of politics into the reality that citizens see every day"; and "the study of government decision making, the analysis of the policies themselves, the various inputs that have produced them, and the inputs necessary to produce alternative policies."
Public Administration
Weber's wide-ranging contributions gave critical impetus to the birth of new academic disciplines such as sociology and public administration as well as to the significant reorientation in law, economics, political science, and religious studies.
Sung Ho Kim, "Max Weber", The Stanford Encyclopedia of Philosophy (Fall 2012 Edition), Edward N. Zalta (ed.)
Public Administration
Decision theory can be pursued not only for the purposes of building foundations for political economy, or of understanding and explaining phenomena that are in themselves intrinsically interesting, but also for the purpose of offering direct advice to business and governmental decision makers. For reasons not clear to me, this territory was very sparsely settled prior to World War II. Such inhabitants as it had were mainly industrial engineers, students of public administration, and specialists in business functions, none of whom especially identified themselves with the economic sciences...
Herbert A. Simon, "Rational decision making in business organizations." Nobel Prize lecture 1978, published in: The American economic review 69(4) (1979): 493-513;