Jams, jellies, marmalade, and preserves are all cooked mixtures of fruit, fruit juices, sugar, and sometimes pectin. (Some fruits contain enough natural pectin to thicken on their own.)
The difference is that some of these spreads have pieces of fruit in them, while others do not. Jelly is a clear spread made from fruit juice, sugar, and sometimes pectin.
Widely used to spread on bread or to fill cakes and cookies, its tender texture is firm enough to hold its shape when released from its container.
Jam is a thick mixture of fruit, sugar, and sometimes pectin that is cooked until the pieces of fruit are soft. The fruit is then purèed, but small, mashed pieces often remain. Preserves are made in the same manner as jam, but the fruit is left in medium to large chunks.
Marmalade is a preserve that contains pieces of citrus fruit peel. The most common variety is made from Seville oranges. Conserves, another type of fruit-based spread, are made from a mixture of fruits, nuts, and sugar. A conserve is often used to spread on biscuits.