Soul food is a term used for an ethnic cuisine. Food traditionnally prepared and eaten by Afrian Americans of the Southern United States. Many of the various dishes and ingredients included in "soul food" are also regional meals and comprise a part of other Southern US cooking, as well.
The style of cooking takes its origins from American slavery. African slaves were given only the "leftover" and "undesirable" cuts of meat from their masters (while the white slave owners got the meatiest cuts of ham, roasts, etc). They also had only vegetables grown for ourselves.
After slavery, many, being poor, could afford only off-cuts of meat, along with offal. Farming, hunting and fishing provided fresh vegetables, fish and wild game, such as possum, rabbit, squirrel and sometimes waterfowl. Africans living in America at the time (and since) made with the food choices they had to work with.
Source : http://en.wikipedia.org/wiki/Soul_food