Well-behaved; obedient—used especially for children and pets; often used as a compliment (e.g., “good boy/girl”).
子犬がお利口に座って私を見ていた。
The puppy sat obediently and looked at me.
先生は授業中に静かだった生徒に『お利口さんだね』と言った。
The teacher said, “Good boy/girl,” to the student who was quiet during class.
赤ちゃんを見て、みんなが『お利口だね〜』と笑った。
Everyone laughed and said, “Such a good baby.”