Jelly is made from sugar, pectin, acid, and fruit juice and is a clear spread that is firm enough to hold its shape. Jellies can also be made from ingredients other than fruit, such as herbs, tea, wine, liqueurs, flowers, and vegetables.
Fruit butter is a smooth and creamy spread that is created by slow-cooking fruit and sugar until it reaches the right consistency; these types of spreads are not always translucent and are often opaque. Fruit butters are best used as a spread and a filling.
Preserves are spreads that have chunks of fruit surrounded by jelly.
Conserves are made with dried fruits and nuts and are cooked. They have a very thick and chunky texture. Conserves work very well as a spread and as a condiment for meats and cheeses.
Marmalade is a citrus spread made from the peel and pulp of the fruit. Marmalades are cooked for a long time and have no pectin, and are used as spreads and glazes.
So what's a gelée? It's just the French word for "jelly."
(Image: Makiko Itoh - thanks!)