Agile

Agile is an approach to building software in short cycles, delivering working software frequently, and changing direction on the basis of what the work reveals — rather than specifying everything up front and executing the specification.

Its premise is that on most projects nobody knows exactly what is needed at the start, including the client, and that a plan is more useful as a hypothesis than as a contract. Building a slice, showing it, and adjusting produces a better result than perfecting the plan.

It is also the most abused word in the industry. "We are agile" is used to mean there is no plan, no written scope and no estimate, which is not agility but the absence of management. Real agile delivery has more discipline than a waterfall project, not less: a prioritised backlog, a fixed cadence, working software at the end of every cycle.