care of idiom
(US in care of); (written c/o)（用来给人留下一个地址，当你不在家时，别人可以通过这个地址联系你）转交
used to give someone the address where you can be contacted when you are staying away from home.
You can write me care of my grandmother. 你可以给我写信，请我祖母转交。