Cracker is a slur used to describe Whites in a derogatory way. This term is said to have originated in England before the 16th century, refering to the lower class whose diet primarily consisted of "crackers", actually biscuits. Many of their descendants were sent to the Georgia penal colony, hence "Georgia crackers.
The word Cracker is a racial slur that has been used historically to degrade and dehumanize whites. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to whites. If you are unsure about whether or not it is appropriate to use the word Cracker, it is best to err on the side of caution and avoid using it in any situation.