Web, domains and email
RDFa
Abbreviation for Resource Description Framework in Attributes
In short and in plain language
RDFa is a way to write details into the code of a page.
The details sit right next to the content. This helps search engines see what the content is. It can be a product, for example.
There are other formats for this too.
Definition
RDFa is a syntax for writing structured data directly into the attributes of a page's HTML code. Search engines can use it to recognise what content means, such as a product or an event. Other formats include JSON-LD and microdata.