from What’s New in 2.0: Roles and Capabilities Dec 1 by Ryan Boren.  I accessed it in January 2013…

wordpress roles and capabilities:  Each role has a set of capabilities. my file OnWordPressRoles
five roles: Subscriber, Contributor, Author, Editor, and Administrator.

A Subscriber has limited capabilities: see the Dashboard and edit his own profile. That is all.

A Contributor can draft posts but cannot publish them.

An Author can publish posts.

An Editor can edit other people’s posts and can manage categories, links, comments, and pages.

An Administrator can do everything: switch themes, activate plugins, edit files, and run importers.

Although these roles seem hierarchical, they are not. Each role is simply a set of
capabilities. The Editor and Administrator roles have the capability to edit posts that do
not belong to them. They can edit anyone’s posts, including each other’s. For those used
to the old user level hierarchy, allowing Editors to modify posts made by Administrators
may seem odd. Avoiding the hierarchy was a purposeful decision, however. You either have
the capability to edit other’s posts, or you don’t.