Cookie jarring is keeping someone as a backup option while you pursue someone else you prefer.
Cookie jarring is dating or stringing along one person as a safety net while you focus your real interest on a different prospect.
The backup, the cookie in the jar, gets just enough attention to stay available in case the preferred option falls through. They are kept warm without genuine commitment.
It is related to breadcrumbing, since both rely on feeding someone small signals to keep them hopeful.
If the effort you get always feels minimal and conditional, you may be the backup. Ask directly where you stand, and be willing to walk if the answer keeps you parked rather than chosen.