What is a cracker?

The term "cracker" was and is used most frequently in the South, especially in Georgia and Florida. Since the 1870s a nickname for Georgia is "The Cracker State", which is displayed proudly with no hint of insult.
Historically the word suggested poor, white rural Americans with little formal education. Historians point out the term originally referred to the strong Scotch-Irish of the backcountry (as opposed to the English of the seacoast). Thus a sociologist reported in 1926, "As the plantations expanded these freed men [formerly bond servants) were pushed further and further back upon the more and more sterile soil. They became 'pinelanders,' 'corn-crackers,' or 'crackers.'" [Kephard Highlanders] Frederick Law Olmsted, an observant Yankee who visited the South in the 1850s, noted that some Crackers "owned a good many negroes, and were by no means so poor as their appearance indicated." [McWhiney xvi]
Usage of the term "cracker" generally differs from "hick" and "hillbilly" because crackers reject or resist assimilation into the dominant culture, while hicks and hillbillies theoretically are isolated from the dominant culture. In this way, the cracker is similar to the redneck.

-Wikipedia