The document discusses various channels of communication within organizations. It defines communication and identifies the basic elements as the sender, message, and receiver. It then describes different types of internal communication channels including formal vertical communication up and down the hierarchy, horizontal communication between peers, and informal grapevine communication. External communication channels with customers, investors, and other external stakeholders are also covered. The key channels of communication discussed are vertical, horizontal, diagonal, formal, informal grapevine, internal, and external.