British-style marmalade is a sweet preserve with a bitter tang made from fruit, sugar, water, and (in some commercial brands) a gelling agent. American-style marmalade is sweet, not bitter. In English-speaking usage "marmalade" almost always refers to a preserve derived from a citrus fruit, most commonly oranges. The recipe includes sliced or chopped fruit peel, which is simmered in fruit juice and water until soft; indeed marmalade is sometimes described as jam with fruit peel (although many manufacturers now also produce peel-free marmalade). Such marmalade is most often consumed on toasted bread for breakfast. The favoured citrus fruit for marmalade production in the UK is the "Seville orange", Citrus aurantium var. aurantium, thus called because it was originally imported from Seville in Spain; it is higher in pectin than sweet oranges, and therefore gives a good set. Marmalade can also be made from lemons, limes, grapefruits, strawberries or a combination.
In Portuguese, according to the root of the word, which is marmelo, "quince", marmelada is a preserve made from quinces. Marmelo in turn derives from Latin melimelum, “honey apple” which in turn derives from Greek μελίμηλον (melimelon).
The Romans learned from the Greeks that quinces slowly cooked with honey would "set" when cool (though they did not know about fruit pectin). Greek melimēlon or "honey fruit"—for most quinces are too astringent to be used without honey, and in Greek "mēlon" or "apple" stands for all globular fruits—was transformed into "marmelo." The Roman cookbook attributed to Apicius gives a recipe for preserving whole quinces with their stems and leaves attached in a bath of honey diluted with defrutum: Roman marmalade.
The extension of "marmalade" in the English language to refer to citrus fruits was made in the 17th century, when citrus first began to be plentiful enough in England for the usage to become common. In some languages of continental Europe a word sharing a root with "marmalade" refers to all gelled fruit conserves, and those derived from citrus fruits merit no special word of their own. Due to British influence, only citrus products may be sold as "marmalade" in the European Union (with certain exceptions), which has led to considerable complaints from those other countries.
The Scottish city of Dundee has a long association with marmalade. The oft-related story of how this came about begins sometime in the 1700s when a Spanish ship with a cargo of Seville oranges docked in Dundee harbour to shelter from storms. A grocer by the name of James Keiller bought a vast amount of the cargo at a knockdown price, but found it impossible to sell the bitter oranges to his customers. He passed the oranges on to his wife Janet who used them instead of the normal quinces to make a fruit preserve. The marmalade proved extremely popular and the Keiller family went in to business producing marmalade. However this is almost complete fiction. The truth is that in 1797, James Keiller, who was unmarried at the time, and his mother Janet opened a factory to produce "Dundee Marmalade", that is marmalade containing thick chunks of orange rind, this recipe (probably invented by his mother) being a new twist on the already well-known fruit preserve of orange marmalade.