directional, measure word, noun, modal particle · inside a specified limit of time, distance, or scope

请在一周内回复我的邮件。

directional, noun, place name · the inner part or interior of a physical space or object

建筑物内禁止吸烟。

directional, noun · relating to the inner or domestic affairs of a country or organization

该国对内实行税收改革，以刺激经济增长。