A WikiTopic is a bunch of content with a name. Every WikiTopic can be viewed in its own page.
A name is almost always a phrase written in PascalCase. For more information about names, including what a fully-qualified name is, see the discussion on TopicName.
The term page is often used synonymously with the term WikiTopic, but properly speaking the page includes everything FlexWiki renders, including the sidebars and navigation links. "WikiTopic" refers only the user-authored part of the page. Another way to think of it is that a WikiTopic is a concept that only has meaning to the FlexWiki software, whereas a page is a generalized web term for "a bunch of HTML that gets rendered by a browser".
A WikiNamespace holds a collection of WikiTopics. In particular, it provides a name "scope" for all of the topics it contains. In other words, all topics are named uniquely within their WikiNamespace. You can have two topics with the same name only if they are in different namespaces. See WikiNamespace for more information.
Other terms you might see that mean the same thing as WikiNamespace are content base, ContentBase, or WikiBase. These are older terms that have been deprecated: although these terms are still in use in places, you should prefer namespace or WikiNamespace.
