I've heard the term missional thrown around for a number of years now, and most of the time I hear it, context is the only way to try to figure out what the author means by it. I've interacted on other blogs with authors, asking for definitions of words at times, and often missional is one of the words I want defined. I'm usually ignored.
A few days ago, I ran across this blog post by Ryan Kelly over on the Gospel Coalition web site. It is by far the most helpful article I've read on missional and missionalarity (that's a new word I just made up...much like others use words in new ways).
I hope you find this as helpful as I did. Use the hyperlinks...there's a lot more additional info buried in those.