Specify the number of executors that this job needs to occupy. Setting this to a bigger value is useful if your job is known to consume multiple threads, so that the scheduling decision is done accordingly — for example, say your job runs tests with 4 threads simultaneously. Specifying 4 makes Hudson schedule your builds to only run on a slave with 4 or more executors, and if your build is then run on a slave with 5 executors, the slave will have just one more available executor, making it that much less likely for Hudson to schedule additional builds on the same node.

Specifying 0 here is the same as specifying 1.