Refers to the special administrative region of China. The spelling マカオ is standard; 澳門 is a rare kanji form.
Macau was once a Portuguese colony.
I plan to travel to Macau next month.
Borrowed from Portuguese 'Macau', possibly derived from the Cantonese name 媽閣 (Maa1 Gok3). The kanji form 澳門 is a Chinese-derived spelling.