Coolness, or being cool, is an aesthetic of attitude, behavior, comportment, appearance, and style that is generally admired. Because of the varied and changing interpretation of what is considered cool, as well as its subjective nature, the word has no single meaning. For most, coolness is associated with exemplifying composure and self-control. When used in conversation, it is often as an expression of admiration or approval, and can be used when referencing both people and items of interest. Although commonly regarded as slang, cool is widely used among disparate social groups and has endured in usage for generations.