W. DeBord's defination is about as specific as you can get unless you have a specific product in mind. There are many different fillings (pastry cream, whipped cream, choc. mousse, fruit mousse, jam, jelly, marmalade, etc.). The list is almost endless. As are the things to fill (eclairs, profiteroles, cakes, doughnuts,etc.)
In French, I believe the proper term, at least for savory fillings would be a "farce". Though I am not absolutely sure of this. Anyone else back me on this? I am not sure the same word would be used to describe a sweet filling. But at least it might give you a start on where to find a translation.