A person on welfare or some other form of government assistance. These people are too lazy to work and spend all day sitting around their crap shack, causing a layer of dust to settle on their back. Related to the term wetback. Can also be applied to those politicians who support them with ridiculous amounts of hard-working taxpayers' dollars.
That octo-mom who won't go get a job is a fucking dustback.
Barack Obama is a dustback enabler.
(For comparison, a dustback enabler is to a dustback what a cocaine dealer is to a crackhead. Incidentally, most crackheads are also dustbacks).