Agile is more than a methodology: it is a collection of methodologies centered on a managerial philosophy—the Agile Manifesto—and set of guiding principles.
Unlike the waterfall model, in an agile model very limited planning is required to get started with the project. Agile assumes that the end users’ needs are ever changing in a dynamic business and IT world.
Changes can be discussed and features can be newly effected or removed based on feedback. This produces regular adaptation to changing circumstances, while allowing customer satisfaction by rapid, continuous delivery of useful products.