First thing that comes to mind is that a cupcake has some form of icing.
Once the icing is off, it can be slightly blurry to which one is which.
Muffins are quick breads whereas cupcakes are little cupped cakes made of cake batter.
Muffins are also a quick bread in the way that they usually cook in more oil than cake
and because of the way they cook in the oil/fat- muffins are usually more coarse.
When it comes to cup cakes- the butter is smoother than oil and with the mixture of butter
and sugar together, it actually creates very tiny air bubbles in the batter to which when the
cake batter is baked- the bubbles expand giving a finer texture than the muffin.
Muffins are more of a breakfast food as well- although I'm sure I'm not the only person
who has ever had a cup cake for breakfast! ...................................SWEET!