Refers specifically to the central bone structure of a fish, often encountered when eating or preparing fish.
この魚は中骨が多くて食べにくい。
This fish has many bones and is hard to eat.
料理の前に中
Please remove the backbone before cooking.
Compound of 中 (naka, 'center') and 骨 (hone, 'bone'), literally meaning 'center bone'.