A term coined by Italian statesman Baldesar Castiglione in his Il libro del cortegiano (1528) to describe an ideal of courtly behavior. Castiglione defined sprezzatura as a style of behavior in which every action "conceals art, and presents what is done and said as if it was done without effort and virtually without thought" (Book 1, Chapter 26). Sprezzatura is usually translated as nonchalance.
Sprezzatura is a contradictory concept, demanding "the ability to show that one is not showing all the effort one obviously put into learning how to show that one is not showing effort" (Berger, 296). Castiglione resolved this paradox of contrived spontaneity by contrasting sprezzatura with affettazione (affectation), which "exceeds certain boundaries of moderation" and must be avoided "in every way possible as though it were some very rough and dangerous reef" (1.27). Affectation draws attention to the effort the courtier makes in maintaining the appearance of taking "no thought in what he is about." Castiglione illustrated the difference between affectation and sprezzatura by contrasting the ungraceful rider who tries "to sit stiff in his saddle (in the Venetian style, as we are wont to say)" with "one who sits his horse as free and easy as if he were on foot."
How much more pleasing and how much more praised is a gentleman whose profession is arms, and who is modest, speaking little and boasting little, than another who is forever praising himself, swearing and blustering about as if to defy the whole world—which is simply the affectation of wanting to cut a bold figure.
Castiglione's Cortegiano was rendered obselete by the rise of absolute monarchs in the 17th century, but sprezzatura remained influential to writers on style and civility. 17th Century French literature made reference to grÃ¢ce, nÃ©gligence and nonchalance. Locke's Thoughts on Education (1693) condemned affectation and praised gracefulness, emphasizing the need to keep a child's spirit "easy."
Ease was incorporated as an equivalent to sprezzatura in the 18th Century formulation of the English gentleman (Burke, 126). Sir Richard Steele's Nestor Ironside persona wrote in the Guardian of the ideal British man: "modest without bashfulness, frank and affable without impertinence, obliging and complaisant without servility" (Guardian #34, 1713). Lord Chesterfield's posthumously published letters emphasized the need to achieve an easy manner and "graceful, noble air" (Burke, 127).
Esquire's Black Book and SF have posts on the subject.
It's worth noting, as it implies a graceful, studied look, but with subtle casual elemets as to appear relaxed, masculine yet most importantly not rigid or effete and affected, or prissy and fussy which I can see when people adhere to rules and are always trying to look perfect.