Cracker, sometimes white cracker, is a pejorative term for white people, poor and Southern whites especially. In reference to a native of Florida or Georgia, however, it is used in a more neutral context.
One theory is that slaver foremen in the antebellum South used bullwhips to discipline African slaves, with such use of the whip being described as 'cracking the whip'. The white foremen who cracked these whips were thus known as 'crackers'.   
Another theory places the word origin in Scotland where a "craic" or "craicker" was a person who talked loudly or boasted. This term was later used to describe white Southerners, particularly those who were poorly educated and possessed little means.
Historically the word suggested poor, white rural Americans with little formal education. Historians point out the term originally referred to the strong English and Scots-Irish farmers of the back country (as opposed to the wealthy planters of the seacoast). Thus a sociologist reported in 1913: "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'."
As early as the 1760s, this term was in use by the upper class planters in the British North American colonies to refer to Scots-Irish and English settlers in the south, most of whom were descendants of English bond servants