Here are a few references from an English-speaking perspective which may help explain:

DEPART: stage start. Nearby is the Tour’s village départ, which gives sponsors and the media the chance to meet VIP guests and, over a coffee and croissant, to chat with one or two of the Tour’s star names. This assembly point is the départ fictif; the rolling start where the starter’s flag drops is termed the départ reel.
http://www.timesonline.co.uk/tol/sport/tennis/article1146600...

Départ: The stage start divides into two separate points. The départ fictif takes place next to the village départ, the start village where the riders are presented and VIPs and hospitality guests gather each morning. This first section is neutral, e.g no rider is allowed to pass the race director's car. The départ réel is the point where race director Christian Prudhomme drops the flag to signal the actual start of the day's racing.
http://www.vorb.org.nz/ftopicp-1791234.html

Mass-start stages
Riders in most stages start together. The first kilometres, the départ fictif, are a rolling start without racing. The real start, the départ réel is announced by the Tour director's waving a white flag.
http://en.wikipedia.org/wiki/Tour_de_France

The French terms usually seem to be left as they are with some sort of gloss.