In general, couture refers to exclusive, custom-fitted fashion made for individual clients. Wikipedia contrasts it with ready-to-wear, which is mass-produced in standard sizes, and notes that couture often involves fine fabrics and detailed hand work.
Haute couture is protected
In France, haute couture is a protected label rather than a style description. The Library of Congress explains that only houses on an official list, drawn up each year by a commission under the Ministry of Industry, may use it. The rules go back to a ministerial order of 1945.
What houses must do
Under that order, a house makes garments to a client’s measurements, in house, with fittings. It must also show two Paris collections a year, in January and July, and create original designs. The Chambre Syndicale de la Haute Couture oversees the process. The Library of Congress notes that the number of accredited houses fell from 106 in 1946 to 16 by 2020. Many couture houses today also sell ready-to-wear and accessories.
Sources: Library of Congress: what haute couture means in French law, Wikipedia: Haute couture
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