A Jump Scar is the jump's visable effect on the universe. When jumping, the teleport will use a hole in space to change locations. This hole takes longer to close than the jump takes, thus resulting in a scar in space.
The scar will eventually go away on its own, but while it is still evident, other jumpers can use it to teleport. Paladins have been known to travel through Jump Scars using a special machine designed to reopen Jump Scars.