Thread:Josephyr/@comment-26521681-20150623232833/@comment-9380534-20150624011226

The main namespace is the default namespace and does not use a prefix in article page names. This is distinct from other namespaces where page names are always prefixed by an indicator of the particular namespace in which the page resides.

For example, all user pages are prefixed by "User:", their talk pages by "User talk:" templates by "Template:" etc... Thus, any page created without such a prefix will automatically be placed in the article namespace.

TLDR - any page that doesn't have a ":" in front of it. ;)