The InternetMonk has a good summary article on missional churches. It will help to better understand what is meant by "missional" in most circles. Some people are antagonistic toward the idea of "missional churches," and some claim that NT churches have always had these ideals even though they did not use the term missional. But most probably don't know much about it. This article will help all three groups.
I will let you read the article rather than trying to summarize it here. But allow me to comment on a couple of things.
First, missional churches are big on the incarnating the gospel, not compromising it. It may be argued that some missional churches do both. The idea of incarnating the gospel is that it is not enough simply to preach the gospel with words; we must also live it in our communities. They would say something like, "Proclamation and Presence." It is not the true gospel if it isn't both. I am increasingly of the opinion that there is much merit in that idea, though I won't defend it here. A "presence" of the gospel in life does not mean the social gospel as we have come to reject it. I think it is different, or at least can be different. But how can we have true faith if we see someone in need and send them away with words? (1 John 3:17-18; James 2:14-17; I know the debate is about who is our brother and whether or not this is a church responsibility, or an individual responsibility. We can hash that out if you want to, or I will talk about it later.)
Second, missional churches talk much about the kingdom using what I believe is a flawed doctrine of the kingdom. Much of their presence is built on a belief of "kingdom now," something that seems manifestly incompatible with what the Bible says about the kingdom. I will simply say that I think the idea of missional churches and incarnation of the gospel does not have to be tied to this faulty view of the kingdom. As a "kingdom not yet" kind of guy, I believe we can be missional, and indeed, we must be missional.
I will write more on this when I return to my series on Evangelistic strategies (that I started a while back). Settling in with the little guy, Easter, and a major evangelistic effort soon arriving has necessitated some delay in that.
This article links to a website by Ed Stetzer called New Churches. The link is in the last paragraph and it won't jump out at you due to formatting. But it is there, or you can click through from here. I haven't look at the site much, but it looks interesting, if for nothing else than to understand where people like Ed are coming from. Ed is the author of a the book Planting Churches in a Postmodern Age. I have read part of it from the library copy, but since I figured the library didn't want me marking their copy up, I ordered my own and it arrived this week. I have found it to be a good book, worth reading.