The MediaWiki software used by Wikitravel lets us split up the site into multiple namespaces. With namespaces, each page is explicitly tagged to show what it's used for and where it fits in the site.
To make a link to an article in a namespace, you use the namespace name as a prefix to the article title, separated by a colon. For example, [[Wikitravel:Help]] is a link to the "Help" article in the "Wikitravel" namespace. See Wiki markup for more information on making links with namespaces.
The namespaces currently in use for Wikitravel are the following:
<Main namespace>. This is where articles in the travel guide go. Links to the main namespace don't use a prefix. For example, [[Switzerland]] is in the main namespace.
Wikitravel:. This is for pages needed to organize our effort. We keep our licensing information, documentation for our software, tools for contributing, explanations of policy, and the style and procedural notes in this namespace, as well as some interactive communication pages like the travellers' pub.
Image: Images uploaded through the upload page will have articles in this namespace. These articles are for describing the rights information for a particular image.
Special: This is for pages that are automatically generated by the MediaWiki software. It's mostly for tools; these pages aren't editable by users.
User: Each registered user on Wikitravel has an associated user page in the User: namespace. The user page for any user is located at User:Name of user. See User page help for details on how user pages work.
Talk: Each article in the main namespace has (or, rather, can have) a corresponding article in the Talk: namespace for discussing the development of that article. See Using talk pages for more information on how these pages are used.
Wikitravel talk: Similar to the Talk: namespace, but associated with pages in the Wikitravel: namespace.
Image talk: Again, a talk namespace, this time for Image: pages.
User talk: Unlike the other talk namespaces, this namespace is for leaving messages for a specific Wikitraveller, rather than for discussing that person.
It usually makes a lot of sense to link from other namespace into the main namespace, but not the other way around.