To do list
Forget about agile methodologies and the agile manifesto. The key idea of agile is "do the most important thing first."
There are lots of methodologies for achieving your goals successfully. There's David Allen's Getting Things Done methodology. There is Stephen Covey's Seven Habits of Highly Successful People. There's the Franklin Planner methodology. And there's Alan Lakein's How to Get Control of Your Time and Your Life, among hundreds of others. But if you boil all these methodologies down, their key observation is that you have a bunch of things to do, and you don't have time to do them all. You have to prioritize and defer or trash the less important ones. How do you address this issue? You write down all your goals, decide which are the most important, label those in some way, and then start working off the top of the list. For example, Covey calls this "First Things First."
Well, that's exactly the workflow of agile. With an agile project, you figure out what features you want to have in your product. Then you rank the features in terms of which are the most important to accomplishing the goals of the release. Then you start working on the most important one. When that's finished, you can work on the next one. It's just like having a To-Do list and marking some things the A's and some things B's and some things C's. Because agile came out of a technical world, and because its proponents are technologists, and not marketers, agile has been presented as a sort of a technical thing. But it's really just a way to bring the familiar "getting things done" approach that any business process consultant will tell you about, to the software development world.