What does "missional" mean?

As I was in the seminary lecture the other day, I used the word "missional" a few times. After one of these times, one of the students asked me to clarify what I meant by that term. That wasn't the first time that's happened to me. I've had pastors, denominational leaders, and even academics ask me what I mean when I use the word.

And while I've read and studied some really good books, and spent a lot of time discussing elements of missional life with a large number of fellow travelers along the way, it's always been difficult for me to define the word in a brief and clear way.

I think part of the difficulty in doing so has to do with how the word sounds. It sounds similar enough to stuff that church people are familiar with that many people make assumptions about what it means - even though more often than not, their assumptions are different than my own definition. It typically takes a few minutes of hearing the word used in a different enough context before people go ahead and ask me for clarification. That's fine - it's a relatively new term, and one that I probably shouldn't throw around too much, because it is confusing.

My biggest problem in defining the word for people is describing its meaning in such a way as to call attention to the differences between what it really means and what it just sounds like it might mean. That, and defining it in a clean enough way that it's quick and simple.

So I think I may start a poll or contest or something to define the word missional in three sentences or less. The definition must be clear, and distinguish substantive differences between assumptions and reality. A metaphor would also be helpful.

I tried looking for the word in Wikipedia, but ran into the problem I have: lack of brevity. Any help out there?

I was reminded of an Albert Einstein quote earlier this week: "You do not really understand something unless you can explain it to your grandmother." Fitting?