It is funny how sometimes you use the lingo without thinking about what it means to someone that doesn't know the lingo. One of our officers brought a relative for a tour and they were explaining that they were going to wait until mass move was finished before they began the tour. She asked, "What is mass move? Is that like where you make everybody get up and exercise?"
I hadn't ever thought of it that way but I guess that is what it sounds like. But no, mass move is when anyone in general population (not maximum security) is allowed to go from one place to another (i.e. from their cell to recreation or class).