Agile

Incremental and iterative improvements done on a regular cadence; an alternative to traditional project management methods, suggests frequent reassessment and adaptation of plans.

— Making Work Visible, Second Edition, Dominica Degrandis

Agile software development is a group of methodologies based on iterative development, where requirements and solutions evolve through the collaboration of self-organizing, cross-functional teams and their customers and end users.

— Project to Product, Mik Kersten

A way of organizing software delivery efforts, first formalized around the early 2000s, that emphasizes constant learning and adjustment. It is often contrasted with “plan-driven” approaches, in which a plan is made in advance and the project team tries its best to stick to the plan. Agile approaches, on the other hand, start from the premise that there are many unknowns and a high likelihood of changing circumstances, and therefore emphasize constant adjustment of the plan to get the best results. The principles of Agile software delivery were articulated in the Agile Manifesto of 2001. Agile has proven to be extremely effective in the digital world, although its principles may seem counterintuitive to those used to classical project management techniques such as Gantt charts and requirements documents.

— War and Peace and IT: Glossary, Mark Schwartz