What are the ways to remove block definitions in a file?

What will be an ideal response?

If you delete a block definition via the Block Manager, all the instances and the block will be removed. Because block definitions are residing in the memory space, even when the instances of the block are deleted or exploded, the block definitions are still in the file. If all the instances of a block definition are removed, either by deleting or exploding, the block is called an unreferenced block. You can remove unreferenced blocks by purging.