A Workflow Job is a runtime representation of a Workflow Process. Each process can have many jobs, each with their own unique id.
Each job uses the current version of the process at the time the job was opened. Therefore, any further changes made to the process by the developer will not affect open jobs.
Once a job is opened, the process will then step through each task until the End Node is reached. Each job can have many tasks, each with their own unique task id.