OK… Let’s focus on the real issue then, rather than having an academic discussion about semantics.
Generically, I’d say you’re going to run into the words “frosting” and “icing” being used for buttercream-type cake coverings. If the recipe isn’t specific about what to cover your cake with (eg, doesn’t have a recipe immediately following with instructions to cover the cake with it), I’d say you’re probably being given creative license for either one. Generally, lighter-type cakes (butter cakes, chiffon, genoise) get a buttercream “frosting” treatment and richer-type cakes (dense spice cake, pound cakes, fruitcake) get an “icing” or glaze-type covering. There are exceptions that prove the rule: Angel food cakes are great with lemon glaze and carrot cakes with cream-cheese frosting rock my world (hold the nuts, IMHO), but I wouldn’t get too fired up about what it’s called and go with your gut about what you prefer and what seems right to you. (Caveat: I wouldn’t recommend you use Royal icing except for small trim or decorating crisp cookies.)
I have a friend that asks for Angel food cake with peanut butter frosting—probably not a combo recommended in the Cake Bible, but that’s what he likes and it’s not as bad as you might think Do use the regular, trans-fatty peanut butter and not the “natural” stuff, though… if you don’t the frosting will slowly slide down the sides of the cake and puddle on the plate.