In modern usage, the term Cotehardie is fairly broad, and can refer to several different garments. For possible definitions, scroll down to Cotehardie in the following external link: Marc Carlson's Glossary
The most common usage of this term in SCA circles refers to a tightly fitted female garment of the 14th to 15th century, which stereotypically has rows of buttons down the front and along the sides of the tightly fitted sleeves.
SCA and modern costume usage, including many popular costume books, typically apply the term "cotehardie" broadly to many fitted female gowns of these centuries. However, costume historian Robin Netherton notes that in period, the term seems to have been far more specialized in meaning. Netherton says that in French and English documents of the late 14th and early 15th centuries, the term most often refers to a short, tight-fitting man's overgown, and while it sometimes occurs (typically in French sources) in reference to a woman's garment, it appears in these cases to refer to a particular style of fitted overdress worn by well-to-do women over a more basic fitted underdress. For that reason, Netherton discourages use of the term "cotehardie" as a generic term for fitted dresses without regard to layer, class, period, or locale, and especially not for the basic fitted underdress (worn over the chemise), which was called a "cotte" or "kirtle" (among other names). Netherton uses the name "Gothic fitted dress" as a modern generic term for the basic fitted style of this period.
Tasha McGann has noted that the common modern perception of the "cotehardie" as having long buttoned sleeves as well as a buttoned front closure is very often a misreading of two layered gowns: an underdress with long buttoned sleeves (the cotte or kirtle) and a short-sleeved fitted overdress with a buttoned front (the form of fitted overdress that Netherton suggests the term "cotehardie" likely referred to). A few isolated examples of dresses with both buttoned front closures and long buttoned sleeves exist in artwork, but these are extremely rare compared to representations of the layered combination.