Publisher Entity
A declared Organization or Person in structured data identifying who stands behind the content.
What it means
Anything deciding whether to trust a claim needs to know whose claim it is. A publisher node states that in a form nothing has to guess at: name, URL, logo, and ideally references to the same entity elsewhere.
The part a short definition leaves out
This belongs in the shared template, not on individual pages. A site where only the blog posts declare a publisher has told machines that the rest of the site was published by nobody in particular.
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.