One interesting factiod is missing from this node - specifically, that the term 'white trash' is what was known as 'black slang'. The black slaves owned by white landowners did not get along well with the white house-servants that they worked alongside. 'White trash' was a disparaging (to say the least) term for a white man who was low enough to take a job as a servant - a job that was clearly so low that a free man would not take it.
"The slaves themselves entertain the very highest contempt for white servants, whom they designate as 'poor white trash.'"
-- Fanny Kemble, journal, Jan. 6, 1833
Since its coinage in the early 1800s, white trash has not evolved much at all. It is most often used in America, where it refers to a poor, blue-collar worker, especially one who lives in an unkempt trailer park and talks with a strong southern accent. In other words, it is a particularly rude word for the already impolite 'redneck'. It is generally recommended that you do not use this term.