Wiki pages in SharePoint 2010 are referred to as fluid pages because, by default, they offer the maximum amount of flexibility in terms of editing, specifically in-place editing. They are an ideal page type for project teams. When a site is provisioned from a Team Site template, the home page of the site is set to type Wiki page by default.
You cannot create Wiki pages in SharePoint Designer; you must create them via the Web interface. In addition, customizing Wiki pages in advanced editing mode in SharePoint Designer is not recommended because this might invoke the Wiki page’s validation mechanism and display a customized status message that is also visible to anonymous users. See