Versions of Backdrop prior to version 1.24.2 included a "position" property for menu items within hook_menu() that contained either the value "left" or "right". For example this menu entry:
$items['admin/config/media'] = array( 'title' => 'Media', 'description' => 'Media tools.', 'position' => 'left', 'weight' => -10, 'page callback' => 'system_admin_menu_block_page', 'access arguments' => array('access administration pages'), 'file' => 'system.admin.inc', );
The 'position' => 'left' property would set the location of the "Media" group of menu items when viewing the "admin/config" administrative page.
This property was removed after it was discovered that the default administration theme Seven does not respect the position value in the first place. So this value has not had an effect within Backdrop sites. Rather than restore the property to make it work, it was decided that using the CSS "columns" property to automatically balance the left/right columns on administration pages would be a better solution while removing an esoteric option from hook_menu().
Any module that uses "position" within hook_menu() should simply delete the line from the code, since it has no effect.