The maximum number of concurrent builds that Jenkins may perform on this agent.

A good value to start with would be the number of CPU cores on the machine. 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.

Agents must have at least one executor. To temporarily prevent any builds from being executed on an agent, use the Mark this node temporarily offline button on the agent's page.

This does not apply to the Jenkins master — setting the number of executors to zero will prevent any builds from being executed on the master.