What are Free Range Chickens

I would like to explore this idea in more depth. I have dogs (Jack Russell Terriers) and i cannot allow my chickens to free range my yard. I have heard about feeding them scraps and left overs, i really tend to save that we early have any left overs. My chickens are not free range as they cannot forge for their own food, but i do let them once in a while but my dogs go crazy.

Definition of Free-Range is :

Free range is a term which denotes a method of farming husbandry where the animals can roam freely for food, rather than being confined in an enclosure^. On many farms, the outdoors ranging area is fenced, thereby technically making this an enclosure, however, free range systems usually offer the opportunity for extensive locomotion and sunlight prevented by indoor housing systems.

But free range in the USA: 
In the United States, USDA free range regulations currently apply only to poultry and indicate that the animal has been allowed access to the outside. The USDA regulations do not specify the quality or size of the outside range nor the duration of time an animal must have access to the outside.