Anonymous user a user who is not logged in to the website. This user only has the ability to view published content.
Authenticated User has several permissions to add content such as a page, news article, event, etc., however, this user may only edit their own content.
Content Editor has the ability to add content and edit all content. This user may also publish and unpublish any content on the site.
Site admin has the ability to alter blocks, menus, paths, and nodes. It is assumed that Site Admin also has the Content Editor permissions.
People Editor role allows one to create, edit, or delete any public profiles.
SEO Editor has all permissions related to SEO. These include administer link checker, meta tags, compliance checker and XML site map. It is assumed this user also has permission of Content Editor.
The taxonomy editor has the ability to edit terms and vocabularies, essentially the categories of the site. This user is assumed to also have Content Editor.