A "jump" is when a person teleports to a different place instantly. Jumping can be done by Jumpers, hence the name.
When a Jumper teleports, he/she is actually opening a hole in the Space-Time Continuum. The hole then moves around the jumper, which is why momentum (i.e. falling) has no effect on the jumper after the jump.
Jumping leaves a shadow of the hole, or a Jump Scar, after the teleport has been performed. This is the jump's effect on the universe. The scar will eventually go away on its own, but while it is still evident, other jumpers can travel throughout it.