Eluvian is a gender element from the element system. It is associated with the element of water, which is considered feminine in alchemy. One whose gender element is purely feminine would be eluvian. The noun form of the word is eluvi (ex: I am eluvi). The term can be combined with other gender terms, such as demieluvian, or eluviboy.
The term eluvian and the flag were made on the Tumblr blog Genderelementarchive on December 23, 2017.
The flag's colors are blue, representing water, and pink, representing femininity. In the center it has an upside down triangle with a dot in the middle- the alchemical symbol for water.