Round kick, sometimes called roundhouse. Bring kicking knee high toward target. Try to get kicking foot high, too, so leg is parallel to ground. Rotate hips away from opponent as the kick moves in an arc attacking from the side of opponent (or if he turns).
In goju foot is pulled back and toes retracted. Point of impact is ball of foot. Retract leg after kicking.
Alternative application is with shin or instep, usually to thigh, head or body.
Basic practice is from a ready (parallel) stance. Pivot standing foot away from target. Bring kicking foot up and arc kick toward center line. Retract leg. Return to ready position. Alternate legs.