Us English jam-makers do have both jelly AND jam. I believe American jelly covers them all? To me, jam is made with the fruit and sugar mixed together and cooked while jelly involves cooking the fruit, straining it and then adding sugar, depending on how much juice, and cooking it. Jellies are good for things like raspberries if you don't like the pips, or apples, because you can cook the whole apple and strain it rather than peeling, coring etc.

Quince and crabapple jelly is lovely. We eat that and straight quince as a jam on bread, but they were used in the past to go with meat.