In Moodle, forum subscription indicates whether you get an email when posts are made to a forum.
From their User Preferences, users can globally elect to subscribe to forums when they post to a forum.
In Moodle, from their Profile drop down in upper right corner, select Preferences, then User.
Select Forum preferences.
Choose desired option from Forum auto-subscribe, Save. If you choose 'No, don't automatically subscribe me to forum posts', you will not receive email notifications when posts are made.