When people think about a missionary they often think of someone who lives in a jungle or some other primitive conditions. While this can be true many people like me live in very modern cities in modern countries. So a missionary cannot be defined just by where or how they live.
Missionaries can be from any one of the five spiritual leadership offices listed in Ephesians 4 (apostle, prophet, evangelist, pastor, and teacher) or even in the helps ministry. But to define a missionary as only being a pastor or evangelist would not be accurate. Sometimes I have difficulty explaining to people that while I am considered a missionary and that I use the term because people understand it, my real calling in the context of Ephesians 4 is that I am a teacher and teaching the Bible is what I am called to do.
So what is a missionary? A missionary is someone sent out and equipped by God. Missionaries live in a variety of places, under a variety of conditions, doing all kinds of work. While every Christian is not sent out to another country, every Christian is called and equipped by God for some "mission" so in one sense of the word everyone is called to be a missionary. Next time you meet or hear about a missionary in another country, find out exactly what God has called them to do; I am sure you will be happy you did.