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.
Only use to set rules in the Template Editor. It shows the string ASSEMBLY for assemblies, PART for parts, and BOLT for bolts, holes, nuts etc. For drawings it shows DRAWING, and for revisions it shows REVISION.