User Level: 

The Token module exposes simple text substitution tokens like [title] and [user-name], for use in path generation, mass mailings, and many other situation where admins want to set up text replacement patterns without using PHP snippets.

Other modules can expose their own domain-specific replacement tokens (like information about a purchase, or an Organic Group that a user is a member of) and use Token's centralized replace() function to replace token occurrences in any piece of text.