The label this rule keeps spares for. Any label a job could ask for works here, including a label expression such as linux && gpu. The field completes labels as you type, offering the labels the AMIs of this cloud carry as well as the labels Jenkins already knows about. The rule applies to every AMI whose labels the expression matches.

Because the templates sharing a label are treated as interchangeable hardware, all the numbers in this rule are counted across that whole group rather than per template. A template's own Minimum number of spare instances is ignored while a rule matches it.