Refers to one of the two external openings of the nose. Common in everyday speech.
右の鼻の穴から血が出た。
Blood came from my right nostril.
鼻の穴が大きい人は、よく息が吸えるらしい。
People with large nostrils seem to be able to breathe in well.
Compound of 鼻 (はな, 'nose') + の (possessive particle) + 穴 (あな, 'hole'). The literal meaning is 'hole of the nose'.