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.

Shows the weld length value entered in the Length box in the weld properties. WELD_LENGTH1 shows the length of the weld above the line and WELD_LENGTH2 below the line.