The semantic web is the umbrella term for the stack of technologies that include RDF, SPARQL, OWL, etc. — it doesn't really have anything to do with HTML, other than some special syntax for embedding RDF into HTML.
I assume there are pockets of existence for these things but for the most part the only time the majority of people encounter anything under the semantic web umbrella is where it has influenced html. It's a tomato is a fruit or vegetable thing, it is technically fruit but to most people it is effectively a vegetable.
> I see someone has sneakily added ActivityPub to the end of the list on wikipedia in 2021, retroactively giving them a success.
Why retroactively...?
The point of these standards is that they all build on top of each other. ActivityPub builds on JSON-LD which is a variant of RDF which uses the existing RDF schemas to define its attributes.
The different bits of the stack are used in many different ways. RDF datasets are really common in many different academic fields and ontology composition (which has always been a thing) has pretty much been subsumed by the semweb standards.
Semweb standards are also the most common standard in graph databases.
New W3C standards, such as ActivityPub, appear all the time and usually build on the existing semweb standards.
But I’m not sure I agree on your definition either. Looking at Wikipedia, semantic web is described, first as Web 3.0 (not to be confused with web3) but I remember it more as a dream of late 90s early 2000, where all data lived on internet accessible urls and had semantic markup, than a tech stack.
I find this distinction to be rather ridiculous. They both semantically(heh) proclaim to be the next version of the web. I see there's a bit of an edit war on https://en.wikipedia.org/wiki/Semantic_Web over the one true web 3.
It's just an arbitrary name where people have incremented a number for something they wanted to be the next big thing. Realistically I think you could only really numerically name the next thing after it has actually successfully been adopted.
I actually use these technologies in my day job (and have been for several years), so it's not just a wikipedia look-up for me. Maybe that's why I think of it in more concrete terms.