When most people talk about HTML as being semantic the assumed meaning is unclear but usually meant to convey it relates directly to the content so a block quote is a block of quote. The other is avoidance of presentational description. It's inaccurate but it's a convention

The Semantic Web as envisioned is alive and used in many cases when you are unaware of it meant to be domain specific lexical vocabularies we have them today. The semantics are human to machine readable ideally not about the presentation or function in a browser.

Microformats were referred to as the lowercase semantic web which sought to use a quicker way than XML serialization for similar grouping of ideas. Anybody remember XFN, the extensible Friends Network. Implemented in WordPress fast revolve as extended to existing HTML attributes.

Also how verification works in Mastodon with rel=me