Work Items Overview
Overview
Work Item is a generic term that includes projects, milestones and tasks.
You can view your Work Items in the Work Items module, which contains a centralized view of all related work items, allowing you to access data across projects.
Work Item Types
Programs
A Program work item groups together Project work items. The Program views provide Program Managers top-level aggregated views of projects, with additional capabilities for visibility and reporting.
A Program is not limited to a maximum number of sub-projects.
Projects
Project Icon 
A project is assigned to a project manager and can also be assigned to other team members, such as managers, resources, reviewers, etc. A project may consist of milestones, tasks, or other sub-projects. Although sub-projects are created as part of a parent project, they are considered independent projects that include an independent team and represent a separate deliverable of the project.
A Project can have up to 20,000 sub-objects.
Milestones
Milestone Icon 
According to standard terminology "A milestone is a significant event in the project, such as an event restraining future work or marking the completion of a major deliverable or phase". Wikipedia
AdaptiveWork milestone has two usages:
- a hammock of tasks
- a significant event (empty milestone)
A milestone is typically used as a container of tasks to be completed in order to achieve the milestone’s goals (in terms of content and dates). This methodology enables an instant understanding of every milestone’s status, especially since it is reflected in the project's work items.
You can refer to a milestone as a significant phase or hammock in your project plan, as this needs to be highlighted in the high level overview of your project. By setting a milestone's due date you can make it behave like a date-driven milestone rather than being fully scheduled by its planned work effort.
Tasks
Task Icon 
According to standard terminology "A task is a discrete scheduled component of work performed during the course of a project. A task normally has an estimated duration, start and due date as well as resources. A task can be dependent on other tasks." Wikipedia
Reportable Work Items
A reportable work item is a work item that work performed on can be reported by resources in their Timesheets.
Only reportable work items are included in timesheets.
Example:
You are running a project with three milestones and numerous tasks located under the milestones.
Presume you are interested in the effort spent on only each milestone. You are not interested in conducting detailed reporting at the task level.
- Set the three milestones as Reportable .
Resources assigned to project activities only see the three milestones on their timesheets.
Resources enter their Total Effort for each milestone while reporting. The amount of effort entered equals the effort invested on all individual tasks within the milestone.
To set work items as reportable , set the Reportable switch in the Time Reporting Settings panel of the work item’s Properties Card.
As a result, the Allow Reporting on sub-items switch becomes disabled, indicating that reporting on the sub-work items is automatically prevented.
To define a specific work item as not reportable, uncheck the Reportable switch for that specific work item.
The Allow Reporting on sub-items switch is automatically enabled, indicating that sub-items can be set as Reportable and are added to the Timesheet report.
To exclude the entire project, a specific branch in the project tree, a milestone or hammock task, disable both the Reportable and Allow Reporting on sub-items switches.
Notes:
Check that System Settings include only manually selected work items in the Time Tracking category, and that it is set according to your organization's reporting policy.
A work item must be in Active state in order to be included in a Timesheet.
To add work items in states other than Active to Timesheets, set the relevant System Setting (such as Allow reporting hours on draft work items) in the Time Tracking category.