The term "missional" has become a popular buzz word among evangelicals. Unfortunately it has become misused and abused. However, I like the term. I believe it succinctly articulates the kind of mindset every disciple of the Lord Jesus ought to have. Every Christian is on mission.
What is the mission of every Christian or of every church? Well generally speaking you could boil that down to Jesus' words in the great commission. You could also quote Jesus from Matthew 5:16 (ESV) and say our mission is to "Let your light shine before others, so that they may see your good works and give glory to your Father who is in heaven." Different people and different churches have said essentially the same thing in their own words and in their own carefully phrased "mission statements" but the mission of every member of the Lord's Church is essentially the same. We are to be a display of God's glory through Christ Jesus.
There aren't two classes of Christian- those who carry out the mission and those that do not. This attitude plays out in churches when you have the hired hands and the consumers. So I'm using the term "missional" to emphasize that every church member is on mission- not just the pastor, not just the missions committee, and not just the really zealous and gregarious people. Those folks may set the pace but every Christian is to be a disciple-maker and a display of God's glory.