Marmalade is a kind of jam, but not just any jam. It is made from citrus fruit — oranges most of all, also lemons or grapefruit — and you can usually see bits of the peel in it. British people eat it at breakfast, spread on toast. It often tastes more bitter than strawberry jam, and that bitter taste is part of the idea, though actually some supermarket jars are quite sweet. A story you may hear is that the name comes from French “Marie est malade” (“Mary is ill”), about Mary, Queen of Scots being given the stuff when she was sick. That is a folk tale, not the real history: the word comes from Portuguese marmelada, a jam made from quince, and further back from Greek words for honey and apple. English also has a rare verb “to marmalade,” but the food is the sense you will meet.