An execution queue is a "processor" of jobs; it controls how job instances run. In order to run, every job is assigned to a target execution queue. You can assign a job to an execution queue while configuring the job, and it will be submitted to that execution queue at runtime. The queue controls how many job instances (of all the jobs assigned to the queue) can be running at any one time, the delay between runs, and other settings. Queues can be local to the job, or shared by multiple jobs. When multiple jobs are assigned to the same execution queue, they will share that queue for executing.