The metadata are documents that explain the characteristics of the data. This information includes dictionaries, definitions, classifications, methodology used in the collection and processing of data, etc.
The metadata may often be consulted directly into the web page of a given table. It will be then specific, targeted and limited to the content of the table. The statistics agencies may also provide a complete metadata section on their website. The links on the left leads to those pages.
The metadata in the research reports are a different case. The methods and the concepts used in a specific research usually form a chapter of the research report.