Agile

Agile software development refers to a group of software development methodologies that promotes development iterations, open collaboration, and process adaptability throughout the life-cycle of the project.

Agile methods are a family of development processes, not a single approach to software development. In 2001, 17 prominent figures[5] in the field of agile development (then called "light-weight methods") came together at the Snowbird ski resort in Utah to discuss ways of creating software in a lighter, faster, more people-centric way. They created the Agile Manifesto, widely regarded as the canonical definition of agile development and accompanying agile principles.
Some of the principles behind the Agile Manifesto[6] are:
Customer satisfaction by rapid, continuous delivery of useful software
Working software is delivered frequently (weeks rather than months)
Working software is the principal measure of progress
Even late changes in requirements are welcomed
Close, daily cooperation between business people and developers
Face-to-face conversation is the best form of communication (Co-location)
Projects are built around motivated individuals, who should be trusted
Continuous attention to technical excellence and good design
Simplicity
Self-organizing teams
Regular adaptation to changing circumstances
The manifesto spawned a movement in the software industry known as agile software development.
In 2005, Alistair Cockburn and Jim Highsmith gathered another group of people — management experts, this time — and wrote an addendum, known as the PM Declaration of Interdependence