When a male uses a jelly or preserves as a substitute lubricant to wank off and masturbate. Used either out of desperation for some form of lube or because of a food fetish.
Girlfriend: Hey!! Why does your cock taste like my grandma's homemade jelly again?
Boyfriend: Just suck it. I did a little Jelly Jacking earlier.
When a gang member or affiliated person represents (jacks) two different gang sets. An example of this would be OYs and OGz in the Bronx, New York, who often throw up OY OGz even though they are two completely different gangs.