I believe it means all your units either a ) have moved (no movement point left) or b ) are moving (has a move path).
I don't think it takes cities into account, because sometimes you will intentionally leave cities not building anything to get certain effects (like bonus money or research).
This is right, it means that there are no more "idle" units, all the rest of the units will move at the end of your turn, or is guarding a town or a square.
As far as I remember it have little to do with cities or research. (sometimes my research idles too for some reason)
Sincerely
~ Kongdej
