In computers, asynchronous processes do not keep the same clock. They happen at different times, or at different speeds, and one does not have to wait for the other to finish before it starts. A live phone call is the opposite: both people must be there at once. An asynchronous job on a machine is more like leaving a message: the work runs when it can, while you keep doing something else. Programmers talk about asynchronous requests, downloads, and tasks. Though actually, students in Taiwan may meet the word first in class, not in code — “asynchronous learning,” where you watch the lesson later instead of sitting in the live hour. That is the same idea stretched out of the machine and onto people. The computer sense is the home meaning; the classroom sense is a later, looser use that became very common. The word is technical. In casual talk people often just say “not live” or “in the background.”