Modelling chocolate is a simple paste made from melted chocolate and corn syrup. It gets kneaded into something resembling modelling clay.
It can be used to form braids, borders, embellishments, flowers & figurines, etc. It can be sculpted, shaped or imprinted. It is more malleable than fondant, gum paste, pastillage, etc.
It tastes less sweet than fondant, and has a nicer flavour in general.
Modelling chocolate has a fairly long shelf life – it will keep for several months wrapped in plastic in the fridge.
Here are just a few examples of some fabulous things you can do with modelling chocolate, or at least if you’re a chef of a certain calibre: