Ashi-guruma (足車), the leg wheel.

Nage-waza (throwing techniques), Ashi-waza (foot and leg techniques), Gokyo 3rd set (Dai-sankyo).
Required for: 3rd Dan (black belt, British Judo Association); 4th Dan (black belt, British Judo Association); 5th Dan (black belt, British Judo Association).

About
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Tori's leg bars across uke's knee line and uke is wheeled over it with a strong rotary action of the hands, without the leg ever taking weight.

Step by step (standard right-handed form)
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1. From a right-handed grip, draw your partner forward onto their toes as if beginning a hip throw.
2. Pivot on your left foot, turning your back partway into them, but instead of taking hip contact, raise your right leg and lay it as a bar across the front of their right leg, just below the knee, without resting weight on it.
3. Balance entirely on your bent left leg; the barring leg stays light.
4. Turn both hands and your trunk powerfully to the left, wheeling their floating weight over the barred leg.
5. They rotate over your leg like a wheel over an axle and land on their back to your front left. Keep the sleeve through the landing and step down with the barring leg once they are down.

Key points
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1. The barring leg touches lightly across the knee line
2. Wheel uke over the leg with hands and trunk rotation
3. Balance on the supporting leg through the whole throw

Receiving it
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You are drawn forward and a leg lies across your knee line as a bar; your upper body is wheeled on while your legs stay. The rotation is like tai-otoshi but higher up the leg. Tuck your chin, follow the wheel, and land on your back with your free left arm slapping.

Reference pages elsewhere
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Ashi-guruma on the IJF technique reference (International Judo Federation): https://judo.ijf.org/techniques/Ashi-guruma

From Waza Book: https://wazabook.com/techniques/ashi-guruma/