Forgot to mention that you can also right click on the x to add delete orientation to hotkey or quick favorites. It will delete the currently select custom orientation. Don’t worry you can’t delete the system defined orientations. Side note on quick favorites: The create/delete orientation is assigned per mode. So, if you do it in edit mode(Mesh) it won’t be available in object mode or edit mode(Curve), and yes you can also create orientations in object mode.
