Structured data. There were a bunch of flavors (web schemas, semantic markup, micro formats) but they've all pretty much failed. They didn't fail in the sense o

Structured data. There were a bunch of flavors (web schemas, semantic markup, micro formats) but they've all pretty much failed. They didn't fail in the sense of not working (they're great and they do what they're supposed to really well) but they've not been adopted to an extent where they'd actually be useful for anything besides very basic SEO.