Concurrency is the property that two or more tasks may be interleaved, instead of requiring one task to complete before another begins. Thus async I&#x2F;O would only be distinguishable from sync I&#x2F;O if there were concurrency, i.e., another task can run while the first task is waiting for the completion of that async I&#x2F;O.<p>What you&#x27;re talking about is parallelism, which is the property that more than one task may execute at the same time. That is what Web Workers achieve.