What is the metadata in microblogging platform?
Metadata is an infamously ill-defined term.  Roughly speaking, it's trying to get at a distinction along the following lines: data is the "content" you care about; metadata is other information that is secondary or exists primarily for technical reasons (e.g., addressing information, tags, technical data to facilitate storage or communication).

A classical analogy is postal mail.  The contents of the letter is considered "data".  The addresses on the envelope might be considered "metadata".

Of course, it's just bits, so at some level it's all data.  But when we talk about the data/metadata distinction, we're usually trying to draw a distinction between the main content that users care about, vs secondary information used to enable the system to work.

Again, the term "metadata" is vague, ambiguous, and ill-defined.  Don't expect a precise technical definition of the term.  Instead, if you plan to use this term in communication  and its precise meaning is important, then make sure to state clearly what you mean by metadata and what you do/don't consider to be metadata.



See also https://freedom-to-tinker.com/2008/10/20/what-your-mailman-knows-part-1-2/ and https://freedom-to-tinker.com/2008/10/23/abandoning-envelope-analogy-what-your-mailman-knows-part-2/ for discussion about the use of the term "metadata" in the  privacy context.