Every now and then, one will run across the terms à la bosse and/or d'apres la bosse in reference to that which some art student was doing in the annals of art history. These look very impressive, written as they are in French, but no one ever bothers to explain what either means. So here you are:
"Bosse" simply translates to "bump," which leads us to "with the bump" and "according to the bump." These are (atypically) cute French ways of saying "learning how to draw via carefully executed studies of plaster casts."
In all seriousness, this traditional method is both highly effective and time-tested (it's been used for centuries). D'apres and à la bosse studies used to be the usual first "life drawing" step any student at an Academie or École des Beaux-Arts took, as it was necessary to work one's way up to live nude models. Armed with black charcoal and white paper, the student would observe a cast of a face, torso, foot or what have you for hours (or even days) on end. In the process of trying to capture every indentation, protuberance and nuance of light with one tool, he or she learned a whopping amount about shading, relationships between values and forms, and the sight-size method.
That's it in a nutshell, then. "Bosse" = "bump" = "plaster cast" (in art, anyway). Short phrases that imply a great deal of work to master classic techniques.