The Discussion detail window on the Activities page provides a way for project managers using P6 to communicate with team members who are using P6, P6 Team Member Web, P6 for Android, or P6 for iOS.
A discussion is an exchange of information, such as a question, answer, or general information that is specific to an activity. The messages to and from team members are saved with the activities and are available to anyone who has access to the project. If more than one team member is assigned to the same activity, all messages are captured in the same dialog box for that activity.