A Sender address is a unique identifier for the sender of a message. It is used to identify who the sender of a message is to a recipient. The Sender Address could be a shortcode, longcode, a Facebook Sender ID or an email address. A Channel on the other hand is a group of sender addresses. It serves as a "container" where you can add a bunch of sender addresses that you own and can be used to send a message to a recipient(s).