Within the confines of project management, a schedule milestone, also known as a milestone activity, is an event of great significance within the project schedule. See also milestone. This major event may be a number of possible events, both planned and unforeseen by project management. As a result a schedule milestone may or may not be present on the project schedule prior to the point in time where the schedule milestone occurs. A few examples of unforeseen schedule milestones would be: a sudden and disastrous accident halting a major production or construction effort that is a key part of the project, or the failure to complete a major deliverable. In most cases project management uses schedule milestones to: mark the formal end of iteration, indicate the completion of a project phase, validate a project’s progression, justify work already completed, and mark the successful completion of a major deliverable or deliverable. By definition a schedule milestone has no duration; the completion of the schedule milestone itself takes absolutely no time or work. This may not always indicate that the next phase of a project can be immediately begun though. Key schedule milestones may require senior level project management to review project progress up to the schedule milestone in question before authorization to continue with the next phase of the project can be given.