Allow me to derail this thread even further with a concise explanation!
I like to make and can various fruit spreads every year. It breaks down like this:
JAM: Crushed fruit cooked with sugar as the primary preservative. The fruit ultimately ends up soft and mushy and loses its shape (although there might be some large bits in there still). Spreads smoothly on toast.
JELLY: Exactly like jam, except you filter out the fruit solids before adding the sugar so it ends up see-through. Basically, it's jam made just from the fruit's juice.
PRESERVES: It can be an umbrella term for all sorts of fruit spreads, but sometimes it specifically refers to chunks of fruit preserved in juice. Tends to be chunkier and less spreadable than jam.
CONSERVES: Any jam made from two or more types of fruit.
FRUIT BUTTERS (such as apple butter): They don't actually involve butter. The key difference is instead of gelling the fruit by adding sugar/pectin, they're made by cooking the fruit until it's extremely concentrated. Think really thick applesauce.
MARMALADES: A jelly with pieces of citrus peel in it.
COMPOTES: the key here is the fruit is cooked very, very slowly, so it's extremely smooth, like a puree.