Loanword from English; used in contexts like travel, events, or poetic descriptions. Often interchangeable with 満月 (まんげつ), but フルムーン can sound more stylish or Western.
Tonight is a full moon, so the moon is very bright.
We'll hold a special event on the night of the full moon.
Variant spelling with an interpunct; less common but still seen.
Borrowed from English 'full moon'.