• Summary Activity—A parent activity of several related children activities, milestones, or other summary activities. Only summary activities can contain other plan objects.

• Activity—A specific step within a plan that contains information, such as duration and effort. An activity can be a "child" of a summary activity. An activity can also have one or more associated deliverables.

• Milestones—Either a date marker or a goal measurement, both of which are tracked. A project or program can contain any number of both types of milestones. A goal measurement milestone usually has one or more deliverables associated with it. Information, such as the duration, is calculated based on the deliverables contained by the milestone. Milestones that serve as date markers usually have no duration associated with them and serve as event signalers.

• Sub Project/Program—A separate project or program instance connected to the parent project or program through the plan. The connection enables the overall project or program status to be calculated using the data from the parent and its subprojects. You can create a "placeholder" subproject without actually linking an existing project or program to it. When you link an existing project or program as the subproject that is also known as a child .