what's difference between nostril and nose piercing?
Nostril piercing is just a form of Nose piercing. Nose piercings are of several types like nostril, bridge and septum. Therefore, all the nostril piercings are nose piercings, but not all the nose piercings are nostril piercings! They may be Bridge piercing or Septum piercing as well. These variations of nose piercing depend on the performing area of the nose- nostril piercing is performed in the rim of the nostril whereas the bridge piercing and septum piercing are performed on the surface and curtilage wall respectively.
You may read "Various Types of Nose Piercing", if you want to learn details about nose piercing.