Glossary/Blocks & attributes
Block definition
The reusable master symbol stored once in a drawing — the template every instance of it points back to.
A block definition is the stored template for a reusable symbol (a door, a valve, a title block) — its geometry, its attribute definitions, and its base point — kept once per drawing regardless of how many times it's placed.
You never edit a block definition directly in normal use; you edit it in the block editor, or (for batch changes) push an updated version out to every drawing that has a copy — which is exactly the redefine-and-propagate workflow a tool built for that problem automates.
BlockCopy