It differs from many other cakes by it's white color, which is achieved principally by separating eggs and using only the egg whites. Other sources of color are controlled as well -- light colored butter or other fat, minumal flavorings, and flour that properly bleached -- either by aging or by chemical bleaching.
Often, the usual chemical leavening is enhanced (or replaced) by whipping the egg whites until they are stiff, and gently folding in other ingredients. For this type of leavening to work well, it is useful to have flour that has been made of softer wheat and to include minumal fat in the cake. As a result, angel food cake has a very light texture and subtle flavor.
For cultures in which the traditional garb of a bride is white, the brides cake is often an angel food cake. Angel food cake is not generally dense enough to support the heavy decoration of a wedding cake.