Metadata means data about other data. Tt may include information about the acquisition or publication of the underlying data, or technical aspects like the format of the files, the amount of storage they require,
or of other properties of the data, and whether they are released under a license that permits reuse or not.
A typical example would be bibliographic metadata, in which key properties of formally published materials are collected — author, title, journal, issue, DOI, PubMed ID, PubMed Central ID or a summary of the content of the published item:
What if everyone in the world were in your lab – a 'hive mind' of sorts, but composed of countless creative intellects rather than mindless worker ants, and one in which resources, reagents and effort could be shared, along with ideas, in a manner not dictated by institutional and geographical constraints?
Other common types of metadata include access codes to database entries, e.g. the access number for a gene listed in Gene Bank.
Citizendium itself keeps metadata about each article in a special text file that can be parsed. The article metadata is used to display an article's subpages as gray tabs across the top of each article, and to classify the articles into Workgroups (topic "categories") to help with managing them.