PRON-POSS
(用以代替his or hers，而不指明是男是女;有人认为这种用法不对)
You use theirs instead of 'his or hers' to indicate that something belongs or relates to a person without saying whether that person is a man or a woman. Some people think this use is incorrect.
例句
He would leave the trailer unlocked. If there was something inside someone wanted, it would be theirs for the taking...
他不会给那个活动房屋上锁。里面要是有什么别人想要的东西，他们可以尽管拿。
This child is nobody's child until someone makes her theirs officially.
在有人办理正式手续认领以前，这个孩子不属于任何人。