Action or behavior performed by a group of people acting together (as opposed to individual action); collective behavior.
学校での集団行動はルールを守ることが大切だ。
In school group activities, it's important to follow the rules.
デモでは参加者が集団行動をとった。
At the protest, the participants acted collectively.
野生動物の集団行動は捕食者から身を守るために役立つことがある。
Group behavior in wild animals can help protect them from predators.
彼はいつも集団行動より個人行動を好む。
He always prefers acting individually rather than in a group.