Agile Methods are used in Project Management, when the result isn't clearly defined at the beginning. This is often the case in IT related projects, where requirements change and possibilies are discovered during an ongoing effort.

The very basic idea is to put more effort into the controlling of projects, rather than defining a fixed set of requirements in the beginning. It also does
not follow the traditional phases (Initiate, Plan, Execute, Control, Close) of a project, rather than breaking down the whole effort into several iterations.

External Links:
http://www.agilemanagement.net/