. . .and marmalade. And fruit butter.
For this Difference Between, we can rely almost entirely on the basic definitions alone. Recipes.HowStuffWorks.com, Dictionary.com, BakingBites.com, and TheKitchn.com all have specific definitions on jams, jellies, and preserves that I will summarize here.
FineCooking.com, however, not only provides definitions, but also a picture, that, really, just says it all: