A missionary is usually involved in a cross cultural setting or across geographical boundaries bringing the message of the gospel. YWAM uses many creative ways of transforming spheres of society such as family, beliefs, business, education, government, entertainment and media.
My understanding – when a person has a personal relationship in Christ, (becomes born-again, accepted Jesus as the Messiah and his personal Savior) then he’s a follower of Jesus , the transformation becomes evident and he just can’t help but tell. The gospel is not just FYI but also FYT (for your transformation). “But you will receive power when the Holy Spirit comes on you; and you will be my witnesses in Jerusalem, and in all Judea and Samaria, and to the ends of the earth.” Acts 1:8 So a person who belongs to Jesus can be called a “missionary, a man with a mission” and the person who does not have Christ is a mission field.
When you grew up in a “Christian” setting, hearing the Word many times but no impact in my life, then it becomes a religion, a ritual. So having an encounter with our Lord Jesus and having a growing relationship is being a doer not just hearer, walking the talk, applying those knowledge day by day by the power of the Holy Spirit.