To be short:

• Administrator - Somebody who has access to all the administration features
• Editor - Somebody who can publish posts, manage posts as well as manage other people’s posts, etc.
• Author - Somebody who can publish and manage their own posts
• Contributor - Somebody who can write and manage their posts but not publish posts
• Subscriber - Somebody who can read comments, comment, receive news letters, etc.

Or, for the diehards, on the Wordpress website you can read all about it more precise.