Comment by OkayPhysicist

They also got it wrong in their explanation. To Americans, jelly is jam with the fruit bits filtered out, leading to a homogeneous spread. Jam has crushed fruit, giving it a thicker, uneven texture, and preserves are whole-ass pieces of fruit boiled down in syrup. Marmalade is jam with citrus rinds. As listed here, they are sorted in descending desirability for inclusion in a peanut butter and jelly sandwich.