Microdata is also a thing, and if I'm not mistaken supports the same vocabulary as JSON-LD (schema.org is a good resource).
That said, JSON-LD has the default for a while now, much like how we largely abandoned REST for RPC. I'm not actually sure if microdata is still supported by all the important parsers today, I've defaulted to using LD for any site I've built for clients, especially ecommerce sites where I want Google Search exposure.
Edit: its worth noting the comparison with semantic HTML. Semantic HTML helps define the structure of the markup but not real world context like "this is a product for sale" or "this is a train schedule."
That said, JSON-LD has the default for a while now, much like how we largely abandoned REST for RPC. I'm not actually sure if microdata is still supported by all the important parsers today, I've defaulted to using LD for any site I've built for clients, especially ecommerce sites where I want Google Search exposure.
Edit: its worth noting the comparison with semantic HTML. Semantic HTML helps define the structure of the markup but not real world context like "this is a product for sale" or "this is a train schedule."