Literally: wind – moon – (mysterious) – (degree)
Alternately: Thinking of someone you haven’t seen in a long time; missing a good friend due to long separation. By extension, thinking about or even mourning the death of someone exceptional.
This is a bit of a special case; while 風月 is a standard phrase describing the beauty of nature (specifically a refreshing breeze and bright, beautiful moonlight), 玄度 is actually a person’s name!
This phrase reportedly comes from an early 5th century CE collection of anecdotes, A New Account of the Tales of the World, Chinese Shih-shuo hsin-yu (Japanese 『世説新語』 = Sesetsu shingo). The story is that Liu Yan, invited to a party held by Emperor Jianwen of Jin, commented that it was a shame that the person in question (Chinese pronunciation Xuan Du?) wasn’t present on such a splendid evening.