What is the definition of agile software development?

A group of software development methodologies based on iterative incremental development with self-organizing cross-functional teams who cooperate to define requirements and to implement the solution.

A framework to describe the software development lifecycle activities from requirements specification to maintenance where test planning of the various test levels is done as soon as the test basis is ready.

Testing carried out informally where no formal test preparation or execution takes place, no recognized test design technique is used and there are no expectations for results.

A way of developing software where the test cases are developed, and often automated, before the software under test is developed.