It's a little weird, here's an article that would describe the process of making some if you're curious:

https://www.masterclass.com/articles/how-to-make-easy-homemade-jelly-basic-jelly

I prefer jam in general, but a lot of people find this stuff easier to spread on a pb&j sandwich (like softer untoasted bread) or other uses where a thick texture would make jam more difficult to use but they still want the fruit goo (like filling a pastry with maybe). Usually we would use the word jam to mean like a chunkier fruit preserve, and jelly specifically refers to this stuff.