as a way of thanking sb or paying them for sth they have done 作为（对…的）回报
Can I buy you lunch in return for your help?
感谢你帮忙，我请你吃午饭好吗？
as a response or reaction to sth 作为回应
I asked her opinion, but she just asked me a question in return.
我征求她的意见，她却只是反问了我一句。