indoor是形容词，意思是“户内的，室内的”；an indoor pool.一个室内游泳池。I think perhaps we should go indoors.我觉得也许我们应该进屋里去。indoors是副词，意思是“在户内，在屋里”；keep indoors/stay indoors.呆在家里，不外出（这里keep在口语中是“逗留，住，呆”的意思）。Do you like outside games or indoor game?你喜欢户外运动还是室内运动呢？