If you use a number of tmux windows as part of your daily workflow, you may find that they get to be a bit of a mess from time to time. There are gaps in the numbering and they aren't laid out in the order you'd prefer. The movew command makes it easy to rearrange these windows.
If you have a window indexed at 2 and you want it to be the 4th window, then you can:
:movew -s 2 -t 4
If you have a gap such that the 4th and 5th windows are numbered 4 and 7, then you can focus the 7 window and simply invoke:
:movew
And that window will be reinserted at the next available slot, in this case, window 5.