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Task - In project management, a task is a unit of work or activity needed for progress towards project goals. Typically, a task must be completed by a set deadline. Tasks may be further broken down into assignments or subtasks.
Work breakdown structure (WBS) - A Work breakdown structure is a comprehensive, hierarchical model of deliverables constituting the scope of a project. It details everything a project team is supposed to deliver and achieve. A work breakdown structure categorizes all project elements, or work packages, into a set of groups and may be used to form cost estimates.