Public - anyone with access to the Train App in your gym (if you want to restrict someone's access to this, you will have to delete them from your Train account)
Default - this respects the Plan Restrictions to Class Types in your PushPress Core account (if they can check into that Class Type they can see that Workout Program)
Private - restricted to those on a specific membership, this means that you need to explicitly add someone to this program or they will not be able to see it.