Aivotsex is a sex under the Tubuhive umbrella that is specific to systems. It is a term used to describe non-humans within systems who have sex characteristics that are not describable as male, female, or intersex. This term may be used by any non-human system member to describe the sex characteristics they have within their inner world.
For example, a non-human system member who is partially or fully an animal may have something similar to a faunagenital, making them fit aivotsex better than terms for human sexes. This term is only to be used by those who are non-human system members, and is not to be used by singlets or anyone who is not a system. One with this sex may or may not identify as aivotgender as well.
The name comes from the Finnish word aivot, which translates to 'brain' or 'mind' in English.