A headmate is an "Alter" of someone who has Dissociative Identity Disorder. A headmate is their own person who has split off from the original person's mind, who has their own separate wants, goals, needs, gender, age, etc.

These headmates are usually formed as a coping mechanism, helping the person with DID to survive the traumatic experiences that they have been a victim to. A collection of headmates including the host is called a Multiple/Median System.

Due to the large amount of systems on Tumblr, it has been wrongly labelled as a "Tumblr trend" and been accused of mocking mental illness, despite it being a mental disorder in itself.
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by 6yrhters January 13, 2016
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An alternate personality or identity living in your head. Similar to a roommate or a house mate, but inside your skull. A person who describes themselves as having headmates is saying that they have people living in their heads who they have conversations with.

Some people can claim different ethnicities or sexualities, thus allowing them to join an autonomous caucus (for instance queer or women’s) that they were not otherwise entitled to join.

When they are acting as the personality of one of their headmates, they call this "fronting"

Related to Otherkin, Multiple Systems, and Tumblr social justice activist
I was so out of it I blacked out and one of my headmates took over and drove the car home.
by psuedon April 7, 2013
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Someone who shares a physical body with one or more people, or someone in a plural system. This term was coined by non-traumagenic systems, though it can be used by any kind of plural system.

A headmate is also sometimes known as an alter (though mostly in traumagenic systems), or simply system members.
We got a new headmate today.”
by sonderwrites September 23, 2020
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