This is a template attribute. Template attributes can be used in filtering, or to retrieve data from the model to use in drawings and reports. For example, when you create a report, Tekla Structures replaces the attributes added in the report template with the corresponding object property values.
This template attribute shows if the parts have been bound to grid levels. The attribute returns 1 if the part is bound to a grid level, and 0 if the part is not bound to any grid level.