In addition to the graphic objects used by AutoCAD, there are several types of nongraphical objects stored in drawing files.
These objects have descriptive designations associated with them, for example, blocks, layers, groups, and dimension styles. In most cases, you name objects as you create them, and rename them later. Names are stored in symbol tables. When you specify a named object, you are referencing the name and associated data of the object in the symbol table.