These terms are frequently used in the missions world. You may hear some variety in how they are used, but the definitions below represent a common understanding.
Church planting: Establishing a new body of believers that meets together for fellowship, teaching, worship and prayer. In a missions context, church planters often work in areas with few known believers.
Discipleship: The long-term process of bringing believers to maturity in Christ by modeling and teaching obedience to God’s Word.
Ethnolinguistic people groups: Communities of people distinguished by their unique language and culture (as opposed to geography or political borders).
Evangelism: Sharing with lost people the good news of how they can be saved eternally through what Jesus did for them on the cross.
Lost people: Individuals who have not been saved by grace through faith in Jesus. Lost people may be reached or unreached.
Missionary: Someone who crosses cultural and/or linguistic boundaries in order to share the gospel and make disciples.
Missions: The intentional process of crossing cultural, linguistic and (often) geographic barriers in order to serve, evangelize and disciple people.
Reached people: Individuals who have access to the gospel. With some effort, they could find a believer, church or Bible in a language and cultural context that they understand. Reached people include both believers and lost people.
Reached people group: A people group where at least 2 percent of the population is known to be professing Christians. With some effort, reached people could find a believer, church or Bible in a language and cultural context that they understand. Reached people include both believers and lost people.
Unreached People Group (UPG): A people group where less than 2 percent of the population is known to be professing Christians. Most unreached people do not have access to a believer, church or Bible in a language and cultural context that they understand.
Unengaged People Group (UUPG): An unreached people group where no known church-planting effort is underway.