While similar German words, they are very different sweet things. Streusel is the crumbly butter-flour-sugar topping you find on u003ca href=u0022https://www.recipesfromeurope.com/streuselkuchen/u0022u003eGerman crumb cakeu003c/au003e (Streuselkuchen) while strudel is the Austrian rolled pastry often filled with fruit (such as apples).