What is the proper term for the little triangular windows on the driver’s door and the front passenger’s door of a car? They could be manually opened outward. They have pretty much disappeared from U.S-made cars.
They are called “wing vents.”
Wing Windows.
Unlike the operating system type, these always allowed a breath of fresh air to be directed right where it was needed most. 
I miss mine greatly. 
Lucy
I used to love these on my dad’s 1971 Ford pickup. You could open them so far that would actually act as ramscoops and force air right into the cabin. Cheap a/c on all but the very hottest days.
Holy crap. I completely forgot these things even existed. Where did they go?
We always called them “breeze windows”.
Some automotive engineer decided that we shouldn’t have the ability to choose to drop our gas mileage a notch or two for the sake of ventilation.
Ruining our gas mileage completely by running the A/C would make much better sense.
Lucy
I’ve always heard them called “vent windows.”
They gave Bill Cosby one of his best bits. Someone was bitching him out through one of those and Cosby asked the guy if he remembered his birth.
Dude: What do you mean?
Cosby: Because you’re going to relive it when I pull you through this window.
We call them “wind wings,” and my van has them. This is a good thing because I pulled all the AC out of it (it needs freon, which is environmentally dodgy, it’s expensive to convert to the new refrigerant and the cooling power isn’t as great, plus I live in Oregon and it just isn’t hot enough to justify the expense.) Also, since it’s a cargo van there isn’t any other ventilation aside from the front windows. On hot days I wear a full cotton skirt which I spray down with water. Then I open the wind wings to blow right across the steering wheel and spread my skirt hem along the wheel and hold it there. Instant evaporative cooler! I just have to put the skirt down when I’m passing a semi… 
Another vote for vent windows. The last time I had them was on a 1985 Toyota pickup. They were especially handy for venting cigarette smoke (an option I no longer require, btw).
I would WAG that they were discontinued for economic reasons. It’s cheaper to build and install one big window than a big one and a little one.
I’ll go one better than vent windows. In the early-mid 60’s, pickups had floor vents around ankle height that could be opened up to ventilate the cab. In a day when A/C was an uncommon option in vehicles, these were extremely welcome.
We called them “no-draft” windows.
Agree with the cheap air conditioning and not getting blown around with a window open.
Also good for flicking cigarette ash without it blowing back in your lap or the rear seat. Not that I smoke anymore.
Almost every car and truck now has curved side windows, and curved wind wings are trickier to make. Remember the little rain gutter that used to send water from the windshield up and over the side windows? That quarter inch thing grabbed so much air, that cutting it off boosted the gas mileage by .25 mpg. The fat chrome seam behind the wind wings probably had the same problem.
It cost me $83 ($35 to have what little R12 left in the system removed and $48 for the conversion kit from Schucks) to convert my Toyota pickup from R12 to R134a. It now blows nice cold air even on the hottest days.
“Vent windows” where I grew up in West Texas, too.
Here, they were always known as “quadrant windows”. I liked 'em.
Another vote for “wing window”.
Gone but not forgotten! Everyone I know wishes they had wing windows but not one car mfgr will put one in a car. I guess it’s the curves, as Asknott said. Saves Ford 50 cents on every truck to leave 'em out.
IIRC in the UK they used to be called “quarter lights”.
My Dad had a 1973 Lincoln Town Car that had wing vents. However, they weren’t “wings.”
You would push the switch to lower the window, but the first thing to lower would be a small triangular piece, followed by the entire window if you didn’t stop.
Here’s a good picture of what they looked like. Notice the line at the front of the driver’s window, making the small triangle. That’s the wing window that rolled down first before the window did.
Interesting concept, but IMHO practically useless, as there was no “wing” to direct the flow of air into the car.
Sorry, I’m not much of a fan of those vent windows. They’re a favorite thing for car thieves to break to get into your car. Had only two car break-ins and both times a vent window was busted to get into the car to steal a stereo or just to make a mess of my dashboard. I’m glad they’re not found in any car I now own.
Wind wings