Coffee cake is a sponge cake flavoured with coffee. The term can also be applied to a cake that is intended to be eaten with coffee or tea (like tea cake), offered to guests as a gesture of hospitality, or served as a brunch food. It is 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.

Coffee cakes are generally round and consist of two layers separated by coffee flavoured butter icing, which also covers the top of the cake. Walnuts are a common addition to coffee cakes. (source)