Coffee cake is meant to be eaten with coffee and the American version is usually presented in one layer.
In the United States, coffee cake generally refers to a sweet cake intended to be eaten with coffee or tea (like tea cake). The American variety is presented in a single layer, flavoured with either fruit or cinnamon, and leavened with either baking soda (or baking powder), which results in a more cake-like texture, or yeast, which results in a more bread-like texture. 
