• https://codex.wordpress.org/Plugin_API/Action_Reference/manage_$post_type_posts_custom_column
• https://codex.wordpress.org/Plugin_API/Filter_Reference/manage_$post_type_posts_columns

Pour un plugin :

	public function setTerrainAdminColumn($columns)
	{
		$columns = array_slice($columns, 0, 3, true) + array('realisations' => 'Terrain à vendre / Réalisation') + array_slice($columns, 3, count($columns)-1, true);
		return $columns;
	}

	public function addTerrainAdminColumn($column_name, $post_id)
	{
		if($column_name == 'realisations')
		{
			$etat = get_post_meta($post_id, 'terrain_a_vendre', true);
			if($etat == 'terrains-a-vendre')
			{
				echo 'Terrain à vendre';
			}
			else if($etat == 'realisations')
			{
				echo 'Réalisation';
			}
			unset($etat);
		}
	}

	add_filter('manage_terrains_posts_columns', array( $this, 'setTerrainAdminColumn' ) );
	add_action('manage_terrains_posts_custom_column', array( $this, 'addTerrainAdminColumn'), 10, 2 );