I often think of preserves as being a little more rustic (more fruit solids, sometimes seeds). Marmalade, as far as I know, is restricted to citrus and contains the rinds. To make matters even more complex, there are also conserves, which may contain fresh and dried fruits as well as nuts.

Jam is made with crushed fruit, preserves have chunks of fruit, marmalade is made with the rind & pulp of citrus (the whole fruit cut up). And although you didn't ask, jelly is made with fruit juice and no solids. :)

Technecially, preserves have lower brix (less solids) then jams, but by only a couple of degrees. Large jam manufacturers save money by producing preserves, since they do not have to cook as long to reduce the moisture.

Don't really think there is to much of a difference besides the kind of fruit used... Now jellies use pectin

Don't really think there is to much of a difference besides the kind of fruit used... Now jellies use pectin

Jam and preserve are the same. Marmalade is a preserve containing fruit rind