Big

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Big refers to a headmate who behaves or feels like an adult. While the exact age of a big is often related to the age of the system's body, it is generally at least 18 years old.

Age varying members may refer to their older mindsets as biggin space (in contrast to little space), and younger members may refer to older members as biggins.

Related Terms
Big is often used in contrast with middle and little, which are other common age indicators.

Some systems may use big to mean caretaker.

Age sliding is when a headmate varies in how old they feel, often going back and forth between adult and little, but can be any ages.