block attribute
Short answer
Editable text fields attached to an AutoCAD block reference, used for tags, callouts, and title-block data.
A block attribute (ATTDEF) is a named text field defined inside a block. When the block is inserted, the user is prompted for each attribute's value. Attributes are how title blocks store sheet-specific data (project number, sheet name, revision), and how parts lists pull data out of symbol blocks. ATTEXT, EATTEDIT, and BATTMAN are the everyday tools; .NET reads them via AttributeReference on the BlockReference.