Origin of the Word "Jam"

University of Oxford has asked a pressing question in Oxford Today. Just what is the origin of the word "jam"?

And why is this so important? (Or at least I am imagining that you are asking this question.) Well, obviously it's because of the movie Spaceballs. With the word "jam", we wouldn't have memorable quotes like the following ones:

Raspberry. There's only one man who would dare give me the raspberry: Lone Star!

Radar about to be "jammed."