Capabilities and Nonces – Tuts+ Code Article

When developing a plug-in (and to a lesser extent, themes) you will often find that you want to allow a user to perform various actions: delete, edit or update posts, categories, options or even other users. More often than not you only want certain authorised users to perform these actions. For this, WordPress uses two concepts: roles and capabilities.

via Capabilities and Nonces – Tuts+ Code Article.