Gojko Adzic cites Elisabeth Hendrikson's keynote at the Agile Testing Days – Seven key agile testing practices for releasable software:

"Agile software teams deliver value in the form of releasable software at frequent regular intervals (at least monthly), at a sustainable pace, while adapting to the changing needs of the business. […] Bottom line is delivering releasable software at least monthly. Releasable in this case means that we actually know that it is going what we wanted it to do. Delivering frequently is not let’s ship it and see what happens. It’s not releasable until it’s Done. Done means both implemented and tested."