Definitions of physical entities invariably contain some table mapping a logical member or port name to the location of the desired member. Such is the typical implementation of data structures in traditional programming languages. Non-template definitions have only one table.
Templates discusses how templates affects this view of structures' layout tables. Template definitions introduce table-templates (necessary when members' types and sizes depend on template parameters). Each complete template definition (all arguments supplied) uses follows one table-template to generate a final layout table.