individual
Participant specific anatomical space (for example derived from T1w and/or T2w images). This coordinate system requires specifying an additional, participant-specific file to be fully defined. In context of surfaces this space has been referred to as fsnative.
https://bids-specification.readthedocs.io/en/latest/99-appendices/08-coordinate-systems.html#nonstandard-coordinate-system-identifiers