Jacket
A jacket combines several workables into a single logical unit.
At least one workable is created when starting a job. In some cases however, one workable is branched into several workflows which will independently follow the workflow. A good example is the approval workflow. A single approval workable will branch to multiple workables: one for each person to approve.
A jacket combines those several workables into one unit. A jacket also contains the full history of all referenced workables, and is kept forever. Each workable has always exactly one jacket, while a jacket can reference multiple workables.
You can visualize jackets and workables of a workflow in