Agile as per english dictionary means able to move quickly and easily.
Agile inshort means iterative / incremental development methodology.
- Adaptive planning
- Evolutionary development and delivery
- A time-boxed iterative approach
- Encourages rapid and flexible response to change
In simple terms I called it test based development where requiierement evolves with each iteration
Honestly, last part of setence likes and cherished by all cutomers, think about you being one of them and have all right to say what qualities your desired software should have during the course of development would be big plus.
Agile philosophy push these key items forefornt
- Customer satisfaction by rapid delivery of useful software
- Welcome changing requirements, even late in development
- Working software is delivered frequently (weeks rather than months)
- Close, daily cooperation between business people and developers
- Working software is the principal measure of progress
- Sustainable development, able to maintain a constant pace
- Regular adaptation to changing circumstances