Tellusian is a xenogender from the element system. It is a neutral gender element and is represented by the element of earth. It is not masculine, feminine, or xenine, but still present. It is best compared to neutrois or maverique. Earth is used to represent it, because it has been frequently used to represent neutral concepts, identities, and terms.
The term tellusian and the flag were made on the Tumblr blog Genderelementarchive on December 23rd, 2017.
The flag's colors are brown and green, representing the element of earth. In the center, it has an upside down triangle with a line through it - the alchemical symbol for earth.
Tellusian comes from the Latin word tellus, meaning "earth".