Answer:   Public Queue - is a queue that you define to schedule the delivery of documents that are aimed at multiple different receiving partners. When you define a public queue, the name of the public queue is added to the list of queues you can select when specifying a scheduled delivery method with the Deliver Document By processing action.
Private queues - are queues that contains only delivery tasks that correspond to documents aimed for a specific receiving partner. You define private queues in the profile of the receiving partner.