「外」(soto) means "outside." It refers to a position external to something, in contrast to "中." For example, if you want to say "outside the room," you would use "部屋の外" (heya no soto).

「外(そと)」は「外部(がいぶ)」という意味(いみ)です。「中(なか)」の反対(はんたい)です。例(れい)：「家(いえ)の外(そと)。」