You create blocks by associating objects and giving them a name. You can also attach information (attributes) to a block.
Every drawing file has an invisible data area called the block definition table. The block definition table stores all block definitions, which consist of all information associated with the block. It is these block definitions that are referenced when you insert blocks in your drawing.
After you define a block in a drawing, you can insert a block reference in the drawing as many times as necessary. Use this method to create blocks quickly.
You can create individual drawing files for use as blocks.
The objects in an inserted block can retain their original properties, can inherit properties from the layer on which they are inserted, or can inherit the properties set as current in the drawing.
Block references that contain other blocks are known as nested blocks. Using blocks within blocks can simplify the organization of a complex block definition.
A block library is a collection of block definitions stored in a single drawing file. You can use block libraries supplied by Autodesk or other vendors or create your own.
You can use tool palettes to organize blocks that are stored in one drawing file or separate drawing files.
To reduce the size of a drawing, you can remove unused block definitions. You can remove a block reference from your drawing by erasing it; however, the block definition remains in the drawing's block definition table.