Definition of Wiki category? Can it be used for documentation issues?

What is the definition of Wiki category? I also find a category SWI-Prolog web site and services. But I wonder whether there is a category documentation.

Are documentation questions that refer to an error or a gap on the SWI-Prolog web site manual sections supposed to go into the Wiki category. Or is there a specific category for it?

Problem is, I can even not choose Wiki, so I guess its not for documentation issues.