What does 'jacked' mean when talking abouts cars? Like, 'a car jacked in the back'?

"Ladder bars", aka traction bars were used on performance vehicles with rear leaf springs to counteract the effects of large amounts of torque applied to the rear wheels during rapid acceleration. They had nothing to do with raising the suspension or "jacking up" the rear end. That was usually accomplished by air shocks.

There are "ladder bars" that may be added between the springs and rear axle to jack up the rear, this was mostly a '70s trend you'll see on some classic muscle cars. It doesn't functionally improve aerodynamics or handling to speak of, but if larger than stock tires are installed it gives some extra fender clearance for the big rubber.