概念 (gài niàn) is the neutral, general term for 'concept' — an abstract idea formed in the mind, common in academic and logical contexts. It differs from 观念 (guān niàn), which carries a subjective or social-value sense (outlook, belief), and 理念 (lǐ niàn), which refers to a guiding philosophy or principle. 主意 (zhǔ yi) is more about a concrete idea or plan of action.