Refers specifically to the position, rank, or status of the Japanese emperor. Often used in formal or historical contexts, such as discussions of succession or abdication.
天皇陛下は皇位を継承された。
His Majesty the Emperor succeeded to the imperial throne.
The new emperor ascended the imperial throne.
Discussions are being held regarding imperial succession.
皇太子が皇位を継ぐことになった。
The crown prince came to succeed to the imperial throne.
The emperor abdicated and passed on the imperial throne.
帝位 is a broader, less common term for an emperor's throne (not limited to Japan), whereas 皇位 refers specifically to the Japanese imperial throne.
皇位 (the imperial throne) is a homophone of 高位 (high rank/status) but refers specifically to the emperor's throne, not general high rank.
Compound of 皇 (こう, 'emperor') and 位 (い, 'rank' or 'position'). The kanji 皇 is associated with the Japanese imperial line, and 位 denotes a formal status or seat.