Just as the French have two words for ‘owl’, they also have two words for chestnut, châtaigne and marron. Basically, if a chestnut hull has one nut fruit inside, it's a châtaigne. If there is more than one, or a big one, it's a marron. But don’t confuse them with horsechestnuts, which are also marrons and come from a tree called a marronier...
Marrons are often used in sweets, notably in dried and candied marrons glacés. You especially see them at Christmas time, sold in boxes like chocolates. Collobrières in Provence is famous for them.
Broken leftover pieces from making marrons glacés go into crème de marrons, a sweet chestnut purée sold in tins or in a tube, used in cakes such as Mont Blanc and as a filling for crèpes (much of it comes from the Ardèche).
There’s also a chestnut cake called Ardéchois à la crème de marron.
Images by Allison Meier, Dana Facaros, romainbehar, Crreative commons License