An attribute reference provides an interactive label or tag for you to attach text to a block. Examples of data are part numbers, prices, comments, and owners' names.
You can extract attribute reference information from a drawing and use that information in a spreadsheet or database to produce items such as a parts list or bill of materials (BOM). You can associate more than one attribute reference with a block, provided that each attribute reference has a different tag. You can also define constant attributes. Because they have the same value in every occurrence of the block, AutoCAD does not prompt for a value when you insert the block.
Attributes can be invisible, which means the attribute reference is not displayed or plotted. However, information on the attribute reference is stored in the drawing file.