When a wall is assembled on the floor, the framer places the crown of the stud upward.
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Quand la cloison est assemblée au sol, le charpentier pose les montants avec la partie convexe (l'arc) vers le haut


Explication en anglais:

"The crown of a piece of dimensional rough lumber is the upward arching curvature you see when you look down its narrowest dimensional edge. To see the crown of a common 2 by wall stud or floor joist, you drop one end of the board on the ground and pick up the other end. Rotate the piece of lumber so that the 1.5 inch wide surface is pointing to the sky. As you orient your eye so that you are looking down this finished edge towards the ground, you will almost always see some amount of curvature. It is possible to have a piece of lumber that is perfectly straight or one with very little curvature, but they are few and far between.

As carpenters build a floor or a wall, it is important that they pay attention to crowns. You want the curvature or crowns of all pieces of lumber in a wall or a floor to point the same direction. In the case of floors, you absolutely want the crowns of the joists to point to the sky after the joists are nailed in place. When walls are framed on the ground or a subfloor, carpenters often do the same thing. When the wall is tilted into position, the wall may have a very slight hump in it as the crowns face out instead of inward.
Some lumber may have excessive crowns. In my opinion, a 16 foot long floor joist should have no more than a one-half inch crown. You measure the amount of crown by snapping a chalk line from the two ends of the floor joist along the wide flat face of the lumber. The chalk line, when stretched tightly, represents a perfectly straight line between the two top ends of the joist. The lumber that exists above the chalk line is the crowned aspect of the lumber. Use a tape measure to determine the extent of the crown.

Crowns can create an issue if a severely crowned floor joist is installed next to one that has no or very little crown. As you walk across a floor that has been framed in this manner, you often can feel the actual hump in the floor. Professional carpenters will always check each joist or wall stud for the amount of crown and mark them. The lumber that has severe crowns can be cut into shorter lengths and used for blocking or short structural header beams above doors and windows. "
http://www.askthebuilder.com/NH037_-_Check_for_Crowns_in_Lum...

Les montants de bois (studs) qui composent l'ossature interne d'une cloison sèche (le sandwich en placoplâtre avec l'ossature en bois à l'intérieur, sur laquelle on visse les plaques) ne sont pas toujours droits, rectilignes. Pour éviter d'avoir une cloison gondolée S'ils présentent une courbure, pour éviter d'avoir une cloison gondolée, il faut tous les mettre dans le même sens, la partie convexe de l'arc vers le haut.

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Note added at 11 hrs 33 mins (2005-09-24 06:52:58 GMT)
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Une autre:

"A crown is a hump in the stud that you see when you look down the 1.5 wide edge of a stud. If the crowns do not all point or face the same direction, your wall(s) will be wiggly once drywalled."
http://www.askthebuilder.com/B241_Two_Simple_Closet_Plans_-_...

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Note added at 21 hrs 35 mins (2005-09-24 16:55:11 GMT)
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on peut aussi parler de "montants cambrés" ou "montants gauchis"

"Les montants cambrés ou gauchis dans des cloisons non porteuses peuvent être redressés en sciant les côtés creux au milieu de la cambrure et en enfonçant un coin dans le trait de scie jusqu’à ce que le montant soit aligné"
http://www.cgcinc.com/handbookAssets/PDFs/f/FR_Handbook_1329...
(page 5)