It is what the name of it implies. Sort of like the backbone in humans. And it depends on how the chicken is cut up. As kids, we did not like that part because it has very little or no meat there. We used to get mad because it was often given to us while others got some meat from the chicken.
If you cut it straight down the middle, there will be no backbone. If you just break off all of the parts, before cutting them off, & cut through the rib cage, there will be one. I very eldom cut up a chicken. I buy it already cut up. A whole chicken, I leave whole for roasting it. I used to just save that part for the stock pot to make stock.