In telecommunication, the term asynchronous operation has the following meanings:

1. A sequence of operations in which operations are executed out of time coincidence with any event.

2. An operation that occurs without a regular or predictable time relationship to a specified event; e.g., the calling of an error diagnostic routine that may receive control at any time during the execution of a computer program. Synonym: asynchronous working.

Source: from Federal Standard 1037C and from MIL-STD-188