“Asynchronous communications can be sent at any time without regard to whether or not the receiver is ready. For example, an email is asynchronous.Synchronous communication is a term for time-dependent communications such as a telephone call whereby parties to communication need to be available at the same time.”“What is Asynchronous Communication?”, John Spacey, Simplicable, December 28, 2016 https://simplicable.com/new/asynchronous-communication