Simple definition
A WordPress block is a structured content element with attributes and optional editor controls.
Purpose and use
A WordPress block is a content or layout unit that can be selected and configured in the editor.
How does it work?
Attributes describe its settings. Some blocks save markup, while dynamic blocks calculate their output when displayed.
Example and verification
For an invalid block after editing, identify its source and saved structure before replacing or deleting its content.
Points to watch
Visually similar blocks can come from different components and offer different settings or migration options.
In short
Block type and dependencies matter alongside appearance when planning a site change.