For kosher species of fowl/poultry that have been properly slaughtered according to laws of kosher slaughter and found to be free of any disqualifying injuries/illnesses/blemishes – all edible parts of the animal are permitted for consumption (excluding blood).
Ironically, I answer this question as someone who hasn't eaten meat in 25 years or so.
As long as the blood has been drained, all parts of a kosher bird can be eaten.
As for what constitutes a kosher bird, the birds that are kosher are listed in the Torah and must be slaughtered in a kosher way. Particularly in a liberal Jewish context, there is also the consideration of ethical kashrut, such as determining both how the animal is treated and how the workers are treated.
Poultry is considered meat in the context of kashrut, and traditionally cannot be eaten with dairy.