the element that makes some larger or overarching thing compelling, valuable, or otherwise interesting, as in “Sure we’ve got local sales experts in each region, but our market intelligence is really the jam in the sandwich”; suggests that without said jam, what remains would be as unappetizing as a bread sandwich; see also peanut butter, entirely unrelated in sense but noteworthy in that if deployed at the same time one could create the PB&J of jargon