Asynchrony, in the general meaning, is the state of not being synchronized.
In specific terms of digital logic and physical layer of communication, an asynchronous process does not require a clock signal, in contrast with synchronous and plesiochronous systems.
At the higher data link layer of communication, asynchrony is synonym of statistical multiplexing, such as in packet mode. The information transmission may or may not start immediately as requested by sender, the additional delay being caused by medium congestion. Contrast with example of circuit switched communication, which (once circuit is established) allows immediate start of transfer with a guaranteed bit rate. Confusingly, a communication is often synchronous at the physical layer, while being asynchronous at the data link layer.
In programming, asynchronous events are those occurring independently of the main program flow. Asynchronous actions are actions executed in a non-blocking scheme, allowing the main program flow to continue processing.[1]
In electric motors, an asynchronous motor is a variant where the electromagnetic field turns with a different (higher) speed than the rotor; the difference is called slip.