If you ever wanted not to show an application running in the background in the plank (dock) of elementary OS, it is simple to do that by changing the preferences. Let’s get started immediately.
Hide running Applications on the Plank
1. Press and hold the ‘Control’ key on the keyboard and right-click on the dock.
2. Select ‘Preferences’.
3. Click on ‘Behavior’ tab.
4. Toggle ‘Show Unpinned’ located under the section ‘Item Management’.
5. That’s it. Any running, but unpinned programs will not be shown on the dock.