The Semantic Web is the idea that web content should carry structured, machine-readable meaning so that software agents can reason and act on it, rather than merely rendering pages for humans.
Origin
Articulated for a broad audience by Berners-Lee and colleagues in the 2001 Scientific American article, it extended the original Web from documents-for-people toward data-for-machines.
Why it matters here
The Semantic Web is the bridge era between the read-write web and the Independent Internet. As agents increasingly read and act across the web, the unanswered question becomes control: who owns the compute and data those agents touch. Web 4.0 adds that axis to the decentralization story.