So many different kinds, styles varieties, names…
Frosting… Icing…same thing. No, but really.
Frosting also comes in different shapes and forms, whether it is a smooth spreadable buttercream, or a drizzly glaze, or even a moldable fondant— all are delicious and open to interpretation.
According to Dictionary.com the definition of Frosting is as follows: a sweet mixture, cooked or uncooked, for coating or filling cakes, cookies, and the like; icing. 
This already opens up the very wide world of frosting. Let’s take it apart.
“A sweet mixture”
The largest component of most frostings, icings, fondants, and ganaches (all in the same family), are sweeteners, whether it be powdered/confectioners’ sugar (also known as icing sugar), marshmallows, sugar, corn syrup or even marshmallow fluff. All these ingredients make the variations of frostings sweet. The mixture usually entails some combination of these ingredients; milk or cream, butter, eggs, and flavorings. Different styles call for different combinations of fats and sweeteners and binders (more about this later).
“Cooked or Uncooked”
Some frostings are cooked, and Epicurious gives them the name of boiled icing. According to Epicurious, boiled icing involves slowly pouring a hot sugar syrup or mixture over beaten egg whites and mixed until smooth. Other frostings, like ganaches, also involve heating corn syrup or sugar along with chocolate, to melt the chocolate and create a creamy spreadable texture. Some fondant recipes also require cooking to reach a certain temperature, reminiscent of making candies.
Uncooked recipes just entail mixing butter, powdered sugar and a small amount of milk until smooth. These generally involve stirring and mixing the ingredients until they are combined rather than heating to combine components. Simple buttercream and cream cheese frostings are of the uncooked variety; butter, cream cheese, sugar, vanilla and a little milk (add cream cheese). The most simple glazes are also uncooked, and at its simplest form are combining powdered sugar with milk or cream until the mixture is smooth and liquidy. Even some simple fondant recipes do not involve cooking ingredients to combine or create syrup.
Many varieties come in cooked or uncooked interpretations, so often the lines blur. Buttercreams, fondants, and glazes all come in both categories, depending on the recipe. Though it is interesting to note that in Epicurious’s definition of Frosting: “It can be cooked (as with boiled icing) or uncooked (as with buttercream),” the boiled frosting category looks a lot like Alton Brown’s ClassicButtercream recipe, where a syrup is created (from corn syrup and sugar) and is added to eggs and mixed in with butter. But Epicurious places buttercreams into the uncooked category. This just illustrates the complex world of frosting and how many lines are crossed and distorted, but in the end it is all delicious.
“for coating or filling cakes, cookies, and the like”
Frosting can go anywhere and everywhere; cakes, sugar cookies, inside cupcakes, on top of graham crackers… on spoons and directly into mouths.
Alton Brown during his episode of Good Eats “The Icing Man Cometh” proclaims that cake is only a vehicle for frosting, basically asserting that the frosting makes the cake. Frostings cover the outside of cakes, from top to bottom (most times) and even can line the layers, creating a melding of sweetness. Frosting can go on the outside and the inside of cupcakes for stuffed surprises and intrigue. Sugar cookies topped with a simple uncooked buttercream or a glaze, make for extra fun while decorating and eating. Pastries can be drizzled with cloyingly sweet glazes, to decorate and add another layer of flavor; cinnamon buns, danishes, tarts, etc.
Oh dear, frosting can really go anywhere.
As previously mentioned, icing is another way of saying frosting. Though, according to Alton Brown, most Americans use the word icing over frosting. It also could be a regional thing, like pop instead of soda. But all in all, frosting is synonymous with icing and vise versa.
According to our definition though, frosting is “for coating or filling cakes, cookies and the like,” which definitely encompasses many many different things and combinations. I like to think of ganache, fondant, and glazes to fit into this category of frosting, as mentioned above. Frosting, ganache, fondant and glazes are all varying combinations of very similar ingredients, to do the same basic job; cover (and be scrumptious of course).
Ganache only comes in one variety— chocolate. According to the Epicurious Food Dictionary, ganache is a cooked icing, made with semisweet chocolate and whipping cream (though these probably can be adjusted, dark chocolate and milk, etc). Ganaches are usually very rich, as it is only chocolate and a little cream. Alton Brown brings in vanilla and corn syrup in his recipe of ganache. Either way ganache is a chocolate lover’s dream, rich, smooth and decadent.
Fondants are a little more flexible in terms of ingredients depending on style, taste and sometimes use. CDKitchen.com explains that this kind of icing relies on a mixture of sugar syrup and glucose that is cooked to a very specific temperature and then kneaded, like dough or bread, to a smooth and malleable paste, like this recipe. About.com, part of the New York Times Company, categorizes its fondant recipes as candy.  Epicurious also mentions that fondant is used as both a candy as well as an icing. However, the rest of the definition in its Food Dictionary, is a little different, mainly in its list of ingredients, “fondant is a simple sugar-water- cream of tartar mixture cooked to the soft- ball stage. After cooling, the mixture is beaten and kneaded until extremely pliable… Heating fondant makes it soft enough to be used as an icing to coat large and small cakes.” Some recipes like this one or this one, do not include cooking at all. But one thing we all can agree on is that this candy/icing paste can be colored and flavored according to aesthetic and taste preferences.
Glazes come in both sweet and savory varieties; glazes go on hams but they also coat doughnuts. Glazes are usually thin and glossy as pointed out by Epicurious, and the sweet glazes can be “anything from melted jelly to a chocolate coating.” A pretty generic recipe for a glaze would be something like this.
Now, some of the most popular frostings are buttercream and cream cheese frostings for their general simplicity and potential as flavor ambassadors.
Buttercreams, which can either be the cooked or uncooked variety, rely severely on butter. Most recipes for the buttercream frosting have enormous amounts of butter, which give this kind of frosting its name, like this recipe. The ingredients generally include, butter (lots of it), confectioners’ sugar, and milk or cream, but it could also include eggs. The butter, the fattier and the fresher the better, instills a level of decadence and indulgence. The cooked version tends to be lighter, and more airy and less sweet, whereas the uncooked can become heavy and tooth numbingly sweet. The buttercream frosting is a great base for a huge number of flavorings and colors, and goes well with basically any kind of cake.
Then there are cream cheese frostings which also come in a large number of potential flavors, tend to be associated with very specific cakes (carrot, red velvet…), even though any cake can benefit from cream cheese frosting. To be cream cheese frosting, the icing must have the requisite cream cheese, which would replace some of the butter in a buttercream. Paula Deen’s recipe is always reliable, but in the end it is very simple. The cream cheese in this kind of frosting, cuts the sweetness a little bit and adds a bit of tang, which in some ways can be seen as a savory element. It adds another level to the flavor profile of the frosting on its own, as well as the cake as a whole. The tang goes especially well with cakes that involve fruits (like banana, zuchinni) or vegetables (carrots). This kind of simple cream cheese frosting can be doctored to be many different flavors as well, just like the buttercream assortment.
Not only are there different kinds, styles and techniques to frosting, there are tons and tons of different flavors. Frosting, like ice cream (link to Ice cream foodfact), is a blank canvas, beckoning creative minds and innovative thinkers to produce a wide variety of flavor combinations. They can range from sweet to savory, textured or silky smooth. Some favorites include chocolate, maple, vanilla… the list goes on and on. Extracts can be added, like almond or peppermint, other liquids like coffee and liqueur, or melted ingredients like chocolates, or even other solids like peanut butter and fruits. Food coloring also adds diversity and aesthetic outlets, but not usually flavor. Countless additives can be mixed in or adapted to the wiles of frosting.
And we already know, frosting takes the cake.
Don't forget to check out my sources page for more reading up on frosting. And coming soon will be a recipe page with the links to all of these sweet recipes.
 Epicurious Food Dictionary “Frosting”
 Epicurious Food Dictionary “Boiled Icing”
 Epicurious Food Dictionary “Frosting”
 Alton Brown Good Eats “The Icing Man Cometh: Buttercream frosting”
 Epicurious Food Dictionary “ Ganache”
 About.com “Fondant Recipes: Marshmallow Fondant”
 Epicurious Food Dictionary “Fondant”
 Epicurious Food Dictionary “Glaze”
 Epicurious Food Dictionary “Buttercream”