Jump lines are the theoretical lines that connect jump points aka nodes with each other. Natural distortions in the space-time fabric are the structural basis of a jump line.
Jump lines are affected by space bodies and might twist following the contours of space and change the location of a jump point they connect. Thus, they aren't straight.
Each jump line has energy, which is drawn from the jump-ship proportionally to the energy required to initiate the jump (this energy depends on the size of the ship or its speed; thus, a minimum-energy jump wears less the jump line). When a line has its energy reduced, it connects to a new destination, or entirely disconnects, in which case the ships simply disappear.