Ethics is a system of moral principles. Which means that you try to do what is correct.
Ethical communication encompasses being honest in all communications, keeping confidential information confidential, and not discussing the personal or business situations of others in public or in front of a third party.
I recently was looking at website designers at a technology fair. He was discussing the business problems of another person I knew with one of her former employees. I did not consider this to be ethical communication and chose not to do business with him because of it.