This is the "GlossaryCategoryEntry" form. Its purpose is to create and edit Instance (vs. Category) glossary entries. If a page with that name already exists, you will be sent to a form to edit that page.
Note that Mediawiki page names are case sensitive, with the exception of the first character. As an example, the pages Applecore and Category:applecore reference the same category, but Applecore and appleCore do not. Also note that embedded spaces and undescores ('_') are considered identical. This Apple Core and Apple_Core both reference the same page.