Meaning
This flag stands for the U.S. Outlying Islands, a set of small, mostly uninhabited islands and atolls in the Pacific and Caribbean, such as Wake Island and Midway Atoll. They use the flag of the United States.
The emoji is rare in chat and shows up mostly in geography quizzes, seabird and wildlife conservation posts, and flag collections. For the country itself, the United States flag is the usual pick. “The albatross colonies on Midway are incredible 🇺🇲🐦”