Glossary
What is a military operations area?
A block of airspace set aside for military training such as formation flying, aerobatics and air combat maneuvering. A civil pilot may legally fly through one whether it is active or not, which is exactly why checking its status and staying alert matters: the traffic inside maneuvers without warning.
Also called MOA
That is the whole entry for now. The longer version, with the mechanics and worked examples, is still to be written. See autorotation for how those read once they exist.