Asynchronous (adjective)
Not synchronous; occurring at different times.
Asynchronous (adjective)
Allowing the client to continue during processing.
Asynchronous (adjective)
Having many actions occurring at a time, in any order, without waiting for each other.
Asynchronicity (noun)
The state of being asynchronous
Asynchronicity (noun)
The extent to which something is asynchronous
Wiktionary