The term, used formally as En Charrette, to describe any hasty period of design work. Charettes usually occur at two periods in the design process.
The first is at the start, where several ideas are thrown out quickly and they are worked through only lightly. This gives a direction to the process that will follow. Oftentimes architects and firms will hold a charrette at the start of a competition or job.
The second and more common usage refers to the end of the design process where the designer or designers struggle to complete as much work as possible before the deadline. The origin of the word comes from this meaning.
At the École des Beaux-Arts, students' work was taken to be reviewed on a cart, "charette" in French. As the work was being transported, students would often be making final adjustments and corrections while on the cart. The term "En Charette" hence refers to the very last-minute work students, architects and designers do before deadlines.