I've never heard the term 'free roam' before, but I guess it refers to the tactic of wandering around with a small pack of decoys, looking for birds. When you find an area that birds are working, you set up a small spread, a makeshift blind, and go to it.
Jumpshooting refers to stalking to within range of sitting ducks, jumping them up and shooting them on the rise. It is an effective technique on creeks, small rivers, sloughs, and ponds. As long as you are quiet and stay out of sight you can sneak up quite close to ducks on small water.