Classicism is a type of poem that upholds the ideals, tenets, and principles that originally defined Roman and Greek literature, architecture and art. Through the poetic form, an ancient Greco-Roman philosophy is expressed.
Classicisms emerged during that source period -- ancient Greece and Rome -- and had their first significant revival through work from Charlemagne's court, produced during the 120-year era of the Frankish Empire from about 780 to 900. Later, in 17th- and 18th-century Europe, writers revived the movement and chose forms for their work that which tended towards logic, rationality, and restraint, as opposed to free-form work or more experimental types of writing. For example, Shakespeare was considered an alternative to classicism, while French authors such as Molière, Pierre Corneille, and Jean Racine. Today, poets continue to write classicisms in the style of old Greece and Rome. It is also of note that "a classicism" may be used to refer to a well-known and persisting expression or other idiom.
Example
Eloisa to Abelard by Alexander Pope
In these deep solitudes and awful cells,
Where heav'nly-pensive contemplation dwells,
And ever-musing melancholy reigns;
What means this tumult in a vestal's veins?
Why rove my thoughts beyond this last retreat?
Why feels my heart its long-forgotten heat?
[n] a movement in literature and art during the 17th and 18th centuries in Europe that favored rationality and restraint and strict forms; "classicism often derived its models from the ancient Greeks and Romans"