alt Hacker NewsConcurrency is parallelism and/or asynchrony, simply the superset of the other two.
Asynchrony means things happen out of order, interleaved, interrupted, preempted, etc. but could still be just one thing at a time sequentially.
Parallelism means the physical time spent is less that the sum of the total time spent because things happen simultaneously.
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michaelsbradley • last Friday at 9:57 PM
Asynchrony also practically connotes nondeterminism, but a single-threaded concurrent program doesn't have to exhibit nondeterministic behavior.
careful: in many programming contexts parallelism and concurrency are exclusive concepts, and sometimes under the umbrella of async, which is a term that applies to a different domain.
in other contexts these words don't describe disjoint sets of things so it's important to clearly define your terms when talking about software.