I don't know where you're from, but I have only ever heard somebody use the phrase "white trash" to refer to lower income white people, usually who behave in a trashy manner but not always (wherein a trashy manner means things like wearing wife beaters or raggy clothing, men walking around without shirts on, living in a trailer park--though that alone doesn't necessarily make you white trash, being undereducated and poorly spoken, being bigoted and outspoken, likely being on drugs or drinking too much, or living on disability payments while not being disabled and still hating "welfare" for others, having a criminal record--penchant for fighting, drunk driving, theft, drug dealing, etc, etc).

And it's very much a racist term because it's implying that regular "trash" is not white.