Zin (previously known as Zum) is one of the base metals from the alloy alignment system based on zinc. It represents a gender that is, to some degree, neutral in nature. It is not masculine or feminine but is not a lack of element (tian). Their gender may be in between masculine or feminine or a third group separate from the two, but either way it is not part of either one. It is similar to neutrois. How one expresses or experiences their neutral gender is defined by them. A zin person can have any alignment or presentation.
Zin 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 zum and the plural form was zincum. 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 zin. It's unknown what the plural form of the new term would be.
The flag is based on the color of zinc alloys, as well as being the color normally associated with neutral genders. The symbol used is the alchemical symbol for zinc. The reason behind the use of zinc comes from the coiner claiming zinc to be a relatively unreactive metal and thus "neutral", however this is factually incorrect.