I've always heard it said that the term came into being in the oilfields of West Texas. It seems that the white man's neck turned red while working in the heat!
Redneck is a derogatory slang term used in reference to poor, uneducated white farmers, especially from the southern United States. It is similar in meaning to cracker (especially regarding Georgia and Florida), hillbilly (especially regarding Appalachia and the Ozarks), and white trash (but without the last term's suggestions of immorality).
In recent decades, the term has expanded its meaning to refer to bigoted, loutish reactionaries who are opposed to modern ways, and has often been used to attack Southern conservatives and racists. At the same time, some Southern whites have reclaimed the word, using it with pride and defiance as a self-identifier.
The term characterized farmers having a red neck caused by sunburn from hours working in the fields. A citation from 1893 provides a definition as "poorer inhabitants of the rural districts...men who work in the field, as a matter of course, generally have their skin stained red and burnt by the sun, and especially is this true of the back of their necks".
Y'all be safe now, ya hear!
Lamentations Chapter 5:
1. Remember, O LORD, what is come upon us: consider, and behold our reproach.
2. Our inheritance is turned to strangers, our houses to aliens.
3. We are orphans and fatherless, our mothers [are] as widows.
5. Our necks [are] under persecution: we labour, [and] have no rest.
16. The crown is fallen [from] our head: woe unto us, that we have sinned!
21. Turn thou us unto thee, O LORD, and we shall be turned; renew our days as of old.