The crop is a sack where the birds food is stored before it is processed by the gizzard.
All birds have a crop and its above the brestbone, just below the neck
ABOVE Picture: Full CropPicture below is a picture of a baby with nothing in its crop - sadly this chick had splayed legs and was rejected by the parents and has since perished
An empty crop is not all that common as normally a parent will feed very soon after the crop empties.
You can see the crop is like a deflated balloon of skin on the neck.