is a term describing a period of intense design activity, often immediately preceding a deadline.
A little history:
The term "Charette" (little cart) appeared in the late 1800's. Architecture students at the Ecole Des Beaux-Arts in Paris who needed to rush their designs to their instructors, placed their drawings on a cart which was called a charette. Later the word broadened in meaning and came to describe any intense, short-term design project. Today the word is used by the architectural and design community at large to describe any intense, on-the-spot design effort.
FML, I've been Archi-totured. I am Charrette-ing all nights at Studio.