Agile software development is iterative, with a continual feedback loop that incorporates client input. It is transparent. On-going client critiques assure buy-in at each development stage. The end result is functional, efficient software that meets client expectations. No surprises. 

Waterfall development is linear. A need is outlined, a solution defined. Project development and software build occurs within a siloed process not shared with client . The end product is released. Fingers are crossed. Alarming surprises may occur. The final product may fall short of client needs and expectations.

Knowledge Source: Day of Agile Conference, Cincinnati, OH, July 24, 2015