If you're a Christian, you have a mission.
Your mission fits into God's broader mission, which is to glorify Himself by redeeming all of creation. Our part is to make disciples by proclaiming the gospel of Jesus in word and deed among all people.
A missionary is someone on mission. I know there are some who prefer to reserve the word only for certain people with certain gifting serving in certain ways, but this isn't helpful because it indirectly communicates that some of God's people don't have a mission; as if God were pleased with a class of Christians who sit on the sidelines. When it comes to mission, there are no spectators. No matter how much you read your Bible, pray, worship, fellowship, and give, you cannot follow Jesus and not go.
"As the Father has sent Me, I also send you." –John 20:21
Of course, God doesn't want all Christians to pack up and move to Myanmar. Some, He will lead to faraway places to minister among people who seem to be very different from us. Others will be lead to live and proclaim the gospel in their hometowns. Regardless of location, the activity is the same: we obey God's word, study culture, translate the gospel into that culture, and make disciples.
"Therefore, we are ambassadors for Christ, certain that God is appealing through us. We plead on Christ's behalf, "Be reconciled to God."" –2 Corinthians 5:20
Because we are all on mission, Christians who don't live as ambassadors are still missionaries, they're just bad ones. Anyone who passively consumes culture is a bad missionary. Anyone who isolates himself from people who don't know Jesus is a bad missionary. Anyone who does not verbally proclaim the god news is a bad missionary. Anyone who walks in sin... well, you get the point.
For too long now, missionaries (in the traditional sense) have been telling missionaries (read: all Christians everywhere) that they aren't missionaries (in any sense). Is it any wonder, then, that many of us don't act like we're on mission?