The outer parts of something are the parts which contain or enclose the other parts, and which are furthest from the centre.
He heard a voice in the outer room.
他听到外屋有人声。
burns that damage the outer layer of skin.
损坏皮肤外层的烧伤。
the outer suburbs of the city.
城市远郊。
an old building with solid outer walls.
一幢外墙坚实的老楼。