Setting the System Status for Activities 
You can set a system status for a single activity. For example, the settings you make in Project System Customizing for the material availability check, determine whether the system checks material or PRT availability when you release activities.
If you release activities individually, the system sets the status "Partially released" in the network header.

You can only release an activity which is assigned to a WBS element if the WBS element has the status "Partially released" or "Released".
The activity is released. In the network header, the system status is set to "Partially released".