What is missions?

My younger sister and I had a conversation a few days ago, about what missions was (and wasn't) as well as what made a missionary a missionary:

Websters Dictionay Defines it this way:

Mission -ministry commissioned by a religious organization to propagate its faith or carry on humanitarian work b: assignment to or work in a field of missionary enterprise c (1): a mission establishment (2): a local church or parish dependent on a larger religious organization for direction or financial support dplural : organized missionary work e: a course of sermons and services given to convert the unchurched or quicken Christian faith.

Missionary -a person undertaking a mission and especially a religious mission

Does it get any simpler than that?

Here's my definition - a mission is any work done to advance the Gospel and the Kingdom of God on Earth. And a missionary is a person doing that work.