Communication Channel : This is the total number of potential communication channels between the Stakeholders.
Example : As a Project Manager, you had 7 Stakeholders to communicate with. Hence, you have 28 communication channels. Two new Stakeholders has been added with whom you also need to communicate with. How many communication channels do you have ?
Answer : You have now 7 + 2 + 1 (you as a Project Manager) = 10 Stakeholders. Therefore, the number of communication channels = (10 x (10-1)/2) = (10 x 9)/2 = 90/2 = 45.