What does setMaster `local[*]` mean in spark?

[*]

From the doc:

./bin/spark-shell --master local[2]

The --master option specifies the master URL for a distributed
cluster, or local to run locally with one thread, or local[N] to run
locally with N threads. You should start by using local for testing.

And from here:

local[*] Run Spark locally with as many worker threads as logical
cores on your machine.