Preserves are whole or cut up fruits cooked in a thick sugar syrup.
Citrus preserves are generally called Marmalades.
Preserves and jams must contain at least 45% fruit, the rest is sugar. Citric or similar food acids, corn syrup and dextrose are also permitted. No artificial colors or flavors are allowed.
There are also stringent and complicated USDA grade specifications for each type of pack (such as portion packs and large bulk pack).
Jams are made by cooking the whole fruit with sugar.
Jelly is fruit juice cooked with sugar to form a gel, some fruits and fruit combinations require added pectin in addition to the natural pectin present in the fruit itself.