Diplomacy
Diplomacy is the art and practice of conducting negotiations between representatives of states. It usually refers to international diplomacy, the conduct of international relations through the intercession of professional diplomats with regard to a full range of topical issues. International treaties are usually negotiated by diplomats prior to endorsement by national politicians. David Stevenson reports that by 1900 the term "diplomats" also covered diplomatic services, consular services and foreign ministry officials.
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.
Diplomacy
It would be some time before I fully realized that the United States sees little need for diplomacy; power is enough. Only the weak rely on diplomacy. This is why the weak are so deeply concerned with the democratic principle of the sovereign equality of states, as a means of providing some small measure of equality for that which is not equal in fact. Coming from a developing country, I was trained extensively in international law and diplomacy and mistakenly assumed that the great powers, especially the United States, also trained their representatives in diplomacy and accepted the value of it. But the Roman Empire had no need for diplomacy. Nor does the United States. Diplomacy is perceived by an imperial power as a waste of time and prestige and a sign of weakness.
Boutros Boutros-Ghali, as quoted in Unvanquished : A U.S. - U.N. Saga (1999), p. 198.