Structured Data
Machine-readable statements embedded in a page describing what it is and who published it.
What it means
Usually JSON-LD in a script block. It states in a fixed vocabulary what prose only implies: this is an Article, published by this Organization, on this date, about this subject.
Without it, everything a machine concludes about a page is inferred from the text, and inference is where it starts getting you wrong.
The part a short definition leaves out
Structured data is not a ranking lever and treating it as one leads to markup that describes a page nobody wrote. It is a description. If it describes something the page does not actually contain, that is worse than having none.
Where this comes from
See whether this is costing you anything
The inspection reports on this signal directly, alongside thirty-seven others, and tells you whether it is a quick fix on your site or something deeper.