Tutoring comp sci, you might explain asynchronous communication vs synchronous. The tutor describes them.
Asynchronous communication refers to modes in which the correspondents need not be engaged simultaneously. Email, text messaging, and comment boards facilitate asynchronous communication. In such contexts, the receivers respond at their convenience.
Synchronous communication requires the correspondents to be simultaneously engaged, waiting for incoming messages, reading them as soon as they arrive and responding directly. The motivation for waiting and responding immediately is to continue the stream of communication. A phone call or face-to-face conversation is synchronous communication.
Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.