The expression means to be sociable with others in a moral and ethical way, but not to form a clique with selfish interests. Qun (群) here means the majority, and associating with it means seeking the common good. Budang (不党) means not to form small factions or cliques purely for selfish reasons or private expediency. A similar expression is “be close but not cliquish.” This is a principle of political ethics, and those who have power and are responsible for governing should follow it by working for the public good.

Confucius said, “A man of virtue should act with dignity and not dispute with others; he should be sociable yet not form a clique.” (The Analects)