A derogatory term used to describe any Hispanic typically Mexicans that jump a fence to cross the border into the US, but used by ignorant people to describe all Hispanics, when more proper terms can be used like wet back, mojo, beaner, my favorite gardener.
Boarder Patrol Agent 1: Look there are some wetback crossing.
Boarder Patrol Agent 2: We are in Arizona, here they are fence jumpers.
Guy 1: you heard about Bob?
Guy 2: nah what happened?
Guy 1: he thinks the grass is greener on the other side.
Guy 2: huh?
Guy 1: he's a fence jumper.
Guy 2: ah yeah that's a shame.