E.g. the 10/40 window.
http://m.youtube.com/watch?v=-s9dC_wbFxg&desktop_uri=%2Fwatch%3Fv%3D-s9dC_wbFxg
10/40 Window. Are you Church of the Nazarene, or something?
Never mind. I see that it is a common phraseology when speaking of missions.