Definition: "Delphi Letter," a series of letters written by Plato, discusses various philosophical topics. "The Five Commandments" are an important set of moral principles that guide human behavior. "Delphi Letter" refers to the collection of letters from ancient philosophers such as Plato and Aristotle, which served as a source for their teachings on ethics, metaphysics, and politics. The term is often used in modern contexts to denote a book or work of literature with many themes and ideas.