The meaning varies depending on the context; a common use would be to refer to mutual behaviour within a relationship/ friendship, etc,. Here are a couple of examples: If I help others, there is a good chance that they will help me to sometime. If I am impolite to others, there is a good chance that they might be impolite to me in return. There are other meanings, but it might contravene community guidelines if I mentioned them here, so you had better check in a good online dictionary, if you want.