Candied fruit or nuts have been cooked slowly in sugar syrup until the sugar soaks all the way in. This does two things: it makes them very sweet, and it keeps them from going bad, which is why people did it long before refrigerators. Candied orange peel, candied ginger, candied chestnuts, candied cherries on top of a cake — these are the ones you meet most. The word is an adjective now, but it started as the past form of a verb 'to candy', meaning to cook in sugar. Almost nobody says 'I candied the peel' in daily talk any more, though cooks and recipe writers still do, so the verb is not dead, just quiet. Two other uses to know. American cooking has 'candied yams' (sweet potatoes baked with sugar and butter) which is a hot side dish at Thanksgiving, not a sweet snack. And people use candied for words and feelings: a 'candied smile' or 'candied words' means sweetened on purpose, and therefore probably not sincere — the same suspicion Chinese carries in 甜言蜜語. Remember also that British and American English disagree about candy itself: in Britain 'candy' is mostly the American word for sweets, but 'candied fruit' is normal in both.