What is "comfort class" on TGVs?

What is the context? In the English language pages of of the TGV sites, it is used as a descriptor word with "class". ex. "What comfort class do you want, 1st or 2nd?"

Here's the TGV page from The Man In Seat 61, showing the interiors of the various trains and classes: http://www.seat61.com/tgv.htm#.Vg0oqyuLhlw