Discuss and learn French: French vocabulary, French grammar, French culture etc.
le fond = the bottom
"un fond de [+ liquid]" implies that you have just enough left to covert the bottom of the more adequate recipient .
For wine, we suppose it's a glass or a bottle....
We also use :
"il ne lui restait qu'une goutte de vin rouge"
"goutte" is the literal translation of "a drop" but here it's not an expression in French, when you use "goutte" you really mean a drop, or a teaspoon at maximum.