纪念 (jì niàn) means 'to commemorate' — it focuses on honoring a person or event through an action, object, or ceremony (e.g., a monument, a souvenir). In contrast, 怀念 (huái niàn) and 缅怀 (miǎn huái) are about emotionally missing or cherishing the memory of someone/something, without implying a physical commemoration. 纪念 can also be a noun meaning 'souvenir' or 'keepsake', which the others cannot.