A blog/site owner has the ability to control and assign specific roles to other users. There are five predefined Roles: Administrator, Editor, Author, Contributor and Subscriber. Administrator has access to all the administration features. Editor can publish and manage posts and pages as well as manage other users’ posts, etc. Author can publish and manage his/her own posts. Contributor can write and manage his/her posts but not publish them. Subscriber can only manage his/her profile in the blog.
More detailed information about this is available from WordPress.