Jelly is what you’ll commonly find near the peanut butter at the grocery store. The sweet fruity spread is made by cooking fruit juice with sugar and acid (and sometimes, pectin, the thickening agent that helps jelly, well… gel!). Once the fruit juice mixture gets cooked down, it’s strained to remove any fruit or seeds, leaving you with a smooth, transparent spread free of any solids. Jelly isn't loose like jam and preserves—it's almost gelatin-like. Grape jelly is a classic, but many other fruits are available in jelly form, including apple, strawberry and other berries. Bright green mint jelly is a popular choice with meat!
What is jam?
Much like jelly, jam is also cooked with sugar and acid, but the difference is that it uses fruit (either chopped, crushed, or pureed) instead of fruit juice. Pectin is also sometimes added, but jams tend to be slightly looser in consistency compared to jellies and have more texture from the addition of fruit. Some jams contain seeds, peels, or chunks of fruit, but not always.
What are preserves?
Fruit preserves are a lot like jam, but they’re slightly thicker, thanks to the addition of large chunks or whole pieces of fruit instead of chopped, crushed, or puréed fruit. You’ll usually find large bits of fruit suspended in preserves, as well as seeds, in many cases. Marmalade, which is made with citrus, is considered to be a preserve because it contains parts of the rind as well as the inner fruit and pulp.
https://www.thepioneerwoman.com/food-cooking/cooking-tips-tutorials/a36099621/jelly-vs-jam-vs-preserves/