In the context of Sterling Selling and Fulfillment Foundation, a milestone refers to a significant point in the processing lifecycle of an order that is automatically determined when the order transitions from one status to another. Milestones serve as crucial dates or events that can be used as criteria for monitoring and tracking the progress of an order. They can be configured at the order, order line, and order release levels. When an order line reaches a status marked as a milestone, Sterling Selling and Fulfillment Foundation recognizes it as a milestone reached, even if only a part of the order line reaches that particular status. Essentially, they represent scheduled events that signify the completion of specific phases within a project or the flow of goods.