What makes development "agile"?

Edit: Originally this post was titled "Agile Development as I interpret it"

Currently the company I work for, FEI, has several software-related positions open and in the last few months we interviewed software architects, team leads and project leads. The job descriptions mention a preference for people with experience in the area of "agile development". So when a resume mentioned that the applicant has experience in that area, I asked that person what, according to him or her, makes software development "agile". This blog post is about the answer I would give.

To me, "agile software development" means that you deliver user-facing functionality in a continuous sequence of short iterations [1]. Because of the length of each iteration, you have to limit the scope of the functionality you promise to deliver. If the scope is too broad, it will not fit time-wise.

To limit the scope of functionality is not enough, you also have to limit the scope of design and implementation. In part this is due to the limited duration of each iteration. But as it is uncertain what functionality will have to be supported in the coming iterations, designing and implementing code in this iteration for iterations to come can turn out to be a waste of time.

To limit oneself in scope of design and implementation does not mean you deliver sub-standard code. Because unless the project is scrapped, you will build upon that code in the coming iterations, you will refactor code to be able to support new functionality. So the code better be in good shape and remain in good shape to be able to keep up your pace for iterations to come.

So that would have been my answer, I hope. When I compare my anwer to the Agile Manifesto, I realize it is woefully incomplete. However, I do think that the elements of software development my answer touches upon, are required for it to be called agile software development.