Alum (previously known as Lumi) is one of the base metals from the alloy alignment system based on aluminum. It represents a gender that is, to some degree, fluid or flux in nature. The linity of one's gender changes and/or one's gender fluctuates within its linity. How one expresses or experiences their gender is defined by them. One's expression/presentation may or may not change as well. An alum person can have any alignment or presentation.
Alum was originally coin on December 1, 2018 by Hail, the original owner of the Tumblr blog lgbt-alchemy. At the time it is was called known as lumi and the plural form was alumi. On December 19, 2019 the alloy alignment system was reworked by Tired, the new owner of the blog. In this rework the name of the term was change to alum. It's unknown what the plural form of the new term would be.
The flag is based on the color of aluminum alloys, as well as being based on the colors of the genderfluid flag. The symbol represents the ability to cross gender elements. The reason aluminum was chosen is because it easily bonds with other metals.