I've seen the term used (secondhand) in an architecture program to describe what is essentially a 1-2 day brainstorming session.
In the real world, the idea seems to be to bring together everybody who might be involved -- a bunch of developers, planners, politicians, etc -- and flesh out a few ideas, so that everybody is on a similar page.
The origin of the term is related to
furious, working-to-the-last-minute efforts.
If I had to use a synonym, I'd go with something between "brainstorming session" and "design exercises."