The term Classical has been used in a variety of contexts to describe works that are based on the models of ancient Greece and Rome, or, in non-Western cultures, of an epoch thought to provide patterns for subsequent generations. It is also, perhaps mainly, used to describe works which appeal to reason and order. It is normally distinguished from the term "classic", meaning of enduring worth.
Classicism is generally contrasted with romanticism.
Classical drama, in Western culture, refers to that which conforms to the three Unities, supposedly derived from the Poetics of Aristotle. These are the unity of time, the unity of place and the unity of action; that is, the action of a play should take place within the period of a day, in the same place, and depicting the one story, with no sub-plots.
In European academic usage, "classical music" tends to refer to a specific period, from about the middle of the 18th century to the early years of the 19th. (In popular usage it covers all "serious" or "art" music of whatever period.) It is characterised by clear structures and by emotional restraint.
The classical music of India refers to that based on rāgas and in accordance with their rules.
It is in literature that classicism most contrasts with romanticism, though the typology can be very difficult to apply. In western Europe, the classical mode was at its most influential in the 18th century, and conformed to Alexander Pope's definition of wit: "True with is nature to advantage dressed,/What oft was thought but ne'er so well expressed." (Essay on Criticism)
See separate article.