Windows come in all sizes and can be installed in any direction. Our new place will make use of rectangular windows (the size will be about 18″ x 48″), placed horizontally and vertically to make the best use of natural light while providing privacy.
The images below show the windows used horizontally in the kitchen as almost a backsplash, and vertically to brighten up a galley kitchen (and notice the original container flooring in the first pic!).
image from Numen
both images above from Desire to Inspire
image from Jetson Green
The pictures above use the horizontal windows in the bedroom to provide a little more privacy, while still letting light stream in.
We are also planning to place some horizontal windows really low on the walls (almost floor-level) so that light can come in and the dogs can look out.