The head of government of a country (in Japan generally synonymous with the prime minister).
首相は国会で新しい政策を発表した。
The prime minister announced a new policy in the Diet.
外国の首相と会談する予定だ。
He is scheduled to meet with a foreign prime minister.
首相官邸は首相の公邸兼執務室だ。
The prime minister's official residence is both a home and an office.