WordPress: Roles
Whenever you access a WordPress site, the software considers what you are trying to do: read a post, edit a page, manage categories. Most sites allow you to read posts and pages without logging in. Any other operation you may request is permitted only if your user definition (as identified by login name and password) includes a corresponding capability.
For administrative convenience, WordPress bundles capabilities into collections called roles. By default, these roles are:
Subscriber:
read published posts and pages
Contributor:
all Subscriber capabilities
contribute a post (for review by editor), and edit it before publication
Author:
all Contributor capabilities
contribute a post, publish/unpublish/edit it, and moderate its comments
Editor:
all Author capabilities
contribute/publish/unpublish/edit any user’s post
contribute or edit any page
manage all categories and moderate any comment
read posts and pages which are marked “private”
Administrator:
all Editor capabilities
define users and assign them roles
configure all site options
More info: Role-scoper