There is two types of transit visa:
This type of visa is now comparable to a Schengen visa.
Airport transit visas allow their holders to transit through the international zone of a French airport (without access to the Schengen space) before flying on to their final destination outside the Schengen space.
Special case of transit through two different airports or terminals in Paris: you are allowed to remain in the international zone, but not to go through Immigration control. Therefore, if you change airports or terminals, you will need to apply for a Schengen visa.