A person's legal nationality or citizenship — the country to which someone belongs under the law.
私は二重国籍を持っていません。
I do not have dual nationality.
履歴書には国籍を書く欄がありますか？
Is there a field to write your nationality on the résumé?
国籍を変更するには長い手続きが必要だ。
Changing one's nationality requires a lengthy procedure.
The registration/flag of a ship, airplane, etc. — the country in which a vessel or aircraft is registered.
その貨物船の国籍はパナマだと記録されている。
The cargo ship is recorded as having Panama as its nationality (registry).
飛行機の国籍を確認してから着陸許可を出した。
We issued landing permission after confirming the airplane's registration country.
レース参加者はヨットの国籍を申告しなければならない。
Race participants must declare the nationality (registration) of their yachts.