Gum paste and fondant are both sugar pastes. They are a frosting type of substance that is created to decorate cakes and pastries. Gum paste is produced from dough and sugar. Baker's often refer to it as "sugar dough." It shapes and forms a lot like clay, and is usually used to make flower decorations or some other kind of design. Gum paste can also be smeared, dusted, and tinted. Poured fondants, on the other hand, are used for a whole cake covering, or it can be used as a filling in pastries and candies.
Fondant icing is more for coating. There are two types of fondants. These include poured fondants, which are derived from water and sugar then stirred, and rolled fondants, which are created by melting marshmallows. The main difference between the two is their general purposes are different. Fondants paint the whole cake, while gum paste is used for decorating.