Alpine System:
The overall seriousness of the complete route based on all factors of the final approach, ascent, and descent including length, altitude, cold, exposure, danger, commitment, and technical difficulty. This system originated with UIAA Roman numerals; it is now generally seen with French letters and is increasingly being used worldwide.
F: Facile/easy. Rock scrambling or easy snow slopes; some glacier travel; often climbed ropeless except on glaciers.
PD: Peu Difficile/a little difficult. Some technical climbing and complicated glaciers.
AD: Assez Difficile/fairly hard. Steep climbing or long snow/ice slopes above 50 degrees; for experienced alpine climbers only.
D: Difficile/difficult. Sustained hard rock and/or ice or snow; fairly serious stuff.
TD: Tres Difficile/very difficult. Long, serious, remote, and highly technical.
ED: Extremement Difficile/extremely difficult. The most serious climbs with the most continuous difficulties.