the LDS jargon -

let's face it, mormons are weird. 
we like ourselves though, and we like that we are weird.
we call it peculiar.

Ward: What everyone else would call a "congregation." basically, the people who go to church same place, same time as you. often referred to as "the ward family."

Stake: A  handful of wards.

Companion: Every missionary is assigned a fellow missionary to be with at all times.   They do everything together for the time they are companions. This is for many reasons, one, I'm sure, because God knows spouses need practice. {See "Transfers"}

Elder: What male missionaries are called.  Also, apostles are referred to as Elders. It just so happens that many of them are old too, but that's not why we call em Elders. They just are.


Sisters: What the girl missionaries are called. Also a title given to adult women in the church. "Sister Moffat...etc." {Similarly, men are usually called "Brother" So-&-So...}

Mission: a "trip," usually for 18-24 months, where the missionary dedicates 100% of their time to serving the Lord through service, teaching, preaching, etc. Boys typically leave around 19, girls around 21.  Missions are not a requirement but an expectation.  Missionaries don't talk to their families except through letters so they can focus on their work.

Mission Leadership Positions: The Mission President is in charge of the mission.  He and his wife are often viewed as the "mom & dad" of the mission.  The rest of the leadership positions are filled by regular missionaries within the mission, and the missionaries who fill them change periodically:  Assistants to the President (APs) assist the president in any and every way he asks them to.  Zone Leaders (ZLs) are under the APs, and supervise a number of companionships.  There are a couple of Zone Leaders under each AP.  District Leaders (DLs) are under Zone Leaders and usually supervise 2-4 companionships.  There are a few District Leaders under each Zone Leader. 

Transfers: every 6-8 weeks, when (under the direction of the Mission President) many missionaries change companions and/or switch areas within their mission boundaries (ie moving to different "suburbs" in the western Santiago metropolitan area).eg. add chicago area, etc.