Agile is a philosophy for developing software that is based on the values and principles of the Manifesto for Agile Software Development.

Process models and Agile

While linear process models do not work well with Agile principles and practices, iterative and parallel models do. This is mostly because of the following Agile values

Working software over comprehensive documentation

Customer collaboration over contract negotiation

Responding to change over following a plan

and the Agile principle

Deliver working software frequently, from a couple of weeks to a couple of months, with a preference to the shorter timescale.