Agile is a methodology of organizing your work in a way that everyone will understand their area of responsibility without heavy planning.
The history of Agile methodology began in 2001 when Agile Manifesto was published. In the beginning of the XXI century, 17 people gathered in the Wasatch Mountains of Utah to discuss and decide the future of software development. These people didn’t like the current working process in the majority of companies that was focused on planning and documenting instead of constantly delivering the result and improving the user experience. They created Agile Manifesto that includes several principles which are considered as a foundation for the whole process.
Since then, lots of resemblant frameworks appeared such as Scrum, Kanban, Lean, and Extreme Programming (XP). Each of them meets the core principles of frequent iteration, continuous learning, and high quality in its own way. Scrum and XP are usually applied for software development working process, Kanban is favored by service-oriented teams like IT or human resources.