German mathematical terms like "Nullstellensatz"

Führerdiskriminantenproduktformel.

The notation $G_\delta$ is from German, $G$ for Gebiet, and $\delta$ for Durchschnitt. Strangely enough, the notation for the co-sets, $F_\sigma$, is from French, fermé and somme.

Ansatz. Although I suppose it is used more in physics than in mathematics. I don't know why the translation is not used often, but I guess it has to do something with the fact that in the beginning of the 20th century German was used much more than English in the scientific literature, I believe.