A comic jam is a creative process where one or more comics artists collaborates on drawing or painting one single comic. Often the process is that one artist creates the first page, and then another artist creates the second, and a third does the next, and so on. There is no script that the artists work from, and the content of the comics is improvised. Any given artist working on a comic jam makes a page based solely on what happened on the previous page.
Variations include each artist contributing a single panel, or set of two or three panels, and then passing it on to the next participant.
The cartoonists of the seminal underground anthology Zap Comix were known for contributing a jam comic to each issue of Zap from around issue #3 onward.