@JvmStatic val Default: CoroutineDispatcher (source)

The default CoroutineDispatcher that is used by all standard builders like launch, async, etc if no dispatcher nor any other ContinuationInterceptor is specified in their context.

It is backed by a shared pool of threads on JVM. By default, the maximal level of parallelism used by this dispatcher is equal to the number of CPU cores, but is at least two. Level of parallelism X guarantees that no more than X tasks can be executed in this dispatcher in parallel.