In normal French, this means the same as it does in English. On Ascension weekend (bank holiday on Thursday + pont on Friday = 4 days anywhere but in Paris) it means one of these frustrating traffic jams where you slow down, pick up some speed, slow down again, pick up some speed, and one hour later you've travelled about 20km.
In close second place, and on the same theme, did you know that caisse is a slang word for a car? I didn't ( I thought it was bagnole, but maybe I'm just out of date) until spending a weekend in the country with Understanding Frenchman and 15 of his friends. Clearly he edits his French for me a bit too much the rest of the time!
So, far too many hours on the autoroute today but photos from the gorgeous Charente-Maritime coming soon!