Why are commercial aircraft windows typically oval instead of circular?
It's done mainly for the passengers' viewing benefit in making structural trade offs over total opening area.  For a given area, a round window has less &quot;meat&quot; of fuselage structure between them.   Aesthetically, a round window looks too much like a ship's porthole unless you make it really large, and then it looks like a fish bowl.
So for a given area, a window that is elongated vertically allows for more variation in eye height than a circular one where the viewing area is equally distributed vertically and laterally, and provides more fuselage structure between the windows (important as an inflated tube in circular tension, or under &quot;hoop stress&quot;).
The 787 went with very large passenger windows to take advantage of the carbon structure and bring as much light inside as possible.  But they still stayed with the round-corner vertical rectangular shape so that short and tall people both get a good view.
The CRJ200, as a corporate jet derivative, suffered from very small windows that were set low, and if you're ridden in one and are tall, you have to bend over to see out.  When the follow-on model, the 700, was in development, a lot of work went into moving the windows up and enlarging them so that most people got a decent view (actually it was solved by moving the floor down a bit).
And finally, actually the Gulfstream's windows aren't round, but ovalized horizontally.  This is likely to accommodate lateral seating variations as a priority over vertical variation because of the corporate seating arrangement and is disadvantageous structurally in terms of the fuselage tube's hoop strength.