Zwieback is a form of rusk (hard, dry biscuit or a twice-baked bread) eaten in Scandinavia, Germany, Austria, France, Switzerland, Italy, Slovenia, Croatia and Greece. It is a type of crisp, sweetened bread, made with eggs and baked twice. It originated in East Prussia.
There are two types of zwieback. One type is made by pinching round pieces of dough, placing one piece on top of another, pressing them together by pushing a finger down through both pieces. It is then baked and served as warm soft rolls. This type is identified with Mennonites. The other type is a bread sliced before it is baked a second time, which produces crisp, brittle slices that closely resemble melba toast.
The name comes from German zwei ("two") or zwie ("twi-"), and backen, meaning "to bake". Zwieback hence literally translates to "twice-baked". The French and Italian names, respectively, biscotte and fette biscottate have the same origin, biscotto (biscuit), which also means twice ("bis-") baked (-"cotto").en.wikipedia.org/wiki/Zwieback