The maximum number of concurrent builds that Jenkins may perform on this node.default: 4
A good value to start with would be the number of CPU cores on the machine(see the "Instance Types and Specifications" chapter of "Elastic Cloud Server Product Introduction" get the cpu number).
Setting a higher value would cause each build to take longer, but could increase the overall throughput. For example, one build might be CPU-bound, while a second build running at the same time might be I/O-bound — so the second build could take advantage of the spare I/O capacity at that moment.

For the master, set the number of executors to zero to prevent it from executing builds locally. Note: master will always be able to run flyweight tasks including Pipeline's top-level task.