Coolness is an admired aesthetic of attitude, behavior, comportment, appearance and style, influenced by and a product of the Zeitgeist. Because of the varied and changing connotations of cool, as well its subjective nature, the word has no single meaning. It has associations of composure and self-control (cf. the OED definition) and often is used as an expression of admiration or approval. Although commonly regarded as slang, it is widely used among disparate social groups, and has endured in usage for generations. There is no single concept of cool. One of the essential characteristics of cool is its mutability—what is considered cool changes over time and varies among cultures and generations.
Nick Southgate writes that, although some notions of cool can be traced back to Aristotle, whose notion of cool is to be found in his ethical writings, most particularly the Nicomachean Ethics, it is not confined to one particular ethnic group or gender.
Although there is no single concept of cool, its definitions fall into a few broad categories.