If you refer to someone as a hillbilly, you are saying in a fairly rude way that you think they are uneducated and stupid because they come from the countryside.
英汉词典释义
n.
<美>乡巴佬;土包子
She belted out ballads and hillbilly songs one after another all evening.她整晚一个接一个地大唱民谣和乡村小调。
英英词典释义
Noun
1. a disparaging term for an unsophisticated person