Green’s Dictionary of Slang

(US) the poor white population of the Southern states of the US.

1969		U. Hannerz Soulside 166: White people are being typed by black people, as ‘crackers’, ‘grays’, ‘Whitey’, ‘Mr. Charlie’, ‘ofays’, ‘PWT’ (poor white trash), ‘honkies’, or ‘blue-eyed blond devils’.
1997–2002		Alt. Eng. Dict. 🌐 poor white trash or p.w.t. (noun) This term is pretty self-explanatory. Be careful! It can enrage those who are the recipient of this term.