defined as
dictionary.com
1. Used as a disparaging term for a member of the white rural laboring class, especially in the southern United States.
2. A white person regarded as having a provincial, conservative, often bigoted attitude.
urbandictionary.com
1. redneck
Mildly offensive term for a lower class white person from the southeastern states of the USA. Derives from someone who spent a lot of time on manual labour outside and so received a "red neck" from the sun.
While I know bigoted rednecks not all are. Everyone seems to have their own definition of redneck.