diff -u b/core/modules/field/tests/modules/field_test/field_test.module b/core/modules/field/tests/modules/field_test/field_test.module
--- b/core/modules/field/tests/modules/field_test/field_test.module
+++ b/core/modules/field/tests/modules/field_test/field_test.module
@@ -159,11 +159,11 @@
  * Implements hook_field_widget_settings_form_alter().
  */
 function field_test_field_widget_settings_form_alter(&$element, &$form_state, $context) {
-  $extra = $context['widget']->getSetting('extra');
+  $third_party = $context['widget']->getSetting('third_party_settings');
   $element['field_test_widget_settings_form_alter'] = array(
     '#type' => 'textfield',
     '#title' => t('Widget settings form alter'),
-    '#default_value' => $extra['field_test_widget_settings_form_alter'],
+    '#default_value' => $third_party['field_test_widget_settings_form_alter'],
   );
 }
 
@@ -179,11 +179,11 @@
  * Implements hook_field_formatter_settings_form_alter().
  */
 function field_test_field_formatter_settings_form_alter(&$element, &$form_state, $context) {
-  $extra = $context['formatter']->getSetting('extra');
+  $third_party = $context['formatter']->getSetting('third_party_settings');
   $element['field_test_formatter_settings_form_alter'] = array(
     '#type' => 'textfield',
     '#title' => t('Formatter settings form alter'),
-    '#default_value' => $extra['field_test_formatter_settings_form_alter'],
+    '#default_value' => $third_party['field_test_formatter_settings_form_alter'],
   );
 }
 
diff -u b/core/modules/field_ui/src/DisplayOverviewBase.php b/core/modules/field_ui/src/DisplayOverviewBase.php
--- b/core/modules/field_ui/src/DisplayOverviewBase.php
+++ b/core/modules/field_ui/src/DisplayOverviewBase.php
@@ -348,13 +348,13 @@
       if ($plugin) {
         // Generate the settings form and allow other modules to alter it.
         $settings_form = $plugin->settingsForm($form, $form_state);
-        $extra_settings_form = array();
-        $this->alterSettingsForm($extra_settings_form, $plugin, $field_definition, $form, $form_state);
-        if (!empty($extra_settings_form)) {
+        $third_party_settings_form = array();
+        $this->alterSettingsForm($third_party_settings_form, $plugin, $field_definition, $form, $form_state);
+        if (!empty($third_party_settings_form)) {
           $settings_form['extra'] = array(
             '#type' => 'container',
           );
-          $settings_form['extra'][$field_definition->getProvider()] += $extra_settings_form;
+          $settings_form['extra'][$field_definition->getProvider()] += $third_party_settings_form;
         }
 
         if ($settings_form) {
@@ -531,10 +531,10 @@
 
         // Only save settings actually used by the selected plugin.
         $default_settings = $this->pluginManager->getDefaultSettings($values['type']);
-        $extra_settings = !empty($settings['extra']) ? $settings['extra'] : array();
+        $third_party = !empty($settings['third_party_settings']) ? $settings['third_party_settings'] : array();
         $settings = array_intersect_key($settings, $default_settings);
-        if (!empty($extra_settings)) {
-          $settings['extra'] = $extra_settings;
+        if (!empty($third_party)) {
+          $settings['third_party_settings'] = $third_party;
         }
 
         // Default component values.
diff -u b/core/modules/field_ui/src/Tests/ManageDisplayTest.php b/core/modules/field_ui/src/Tests/ManageDisplayTest.php
--- b/core/modules/field_ui/src/Tests/ManageDisplayTest.php
+++ b/core/modules/field_ui/src/Tests/ManageDisplayTest.php
@@ -101,12 +101,12 @@
 
     // Assert that the field added in
     // field_test_field_formatter_settings_form_alter() is present.
-    $fieldname = 'fields[field_test][settings_edit_form][settings][extra][field_test][field_test_formatter_settings_form_alter]';
+    $fieldname = 'fields[field_test][settings_edit_form][settings][third_party_settings][field_test][field_test_formatter_settings_form_alter]';
     $this->assertField($fieldname, 'The field added in hook_field_formatter_settings_form_alter() is present on the settings form.');
     $edit = array($fieldname => 'foo');
     $this->drupalPostAjaxForm(NULL, $edit, "field_test_plugin_settings_update");
 
-    // Confirm that the extra settings are not updated on the settings form.
+    // Confirm that the third_party_settings settings are not updated on the settings form.
     $this->drupalPostAjaxForm(NULL, array(), "field_test_settings_edit");
     $this->assertFieldByName($fieldname, '');
 
@@ -194,12 +194,12 @@
 
     // Assert that the field added in
     // field_test_field_widget_settings_form_alter() is present.
-    $fieldname = 'fields[field_test][settings_edit_form][settings][extra][field_test][field_test_widget_settings_form_alter]';
+    $fieldname = 'fields[field_test][settings_edit_form][settings][third_party_settings][field_test][field_test_widget_settings_form_alter]';
     $this->assertField($fieldname, 'The field added in hook_field_widget_settings_form_alter() is present on the settings form.');
     $edit = array($fieldname => 'foo');
     $this->drupalPostAjaxForm(NULL, $edit, "field_test_plugin_settings_update");
 
-    // Confirm that the extra settings are not updated on the settings form.
+    // Confirm that the third_party_settings settings are not updated on the settings form.
     $this->drupalPostAjaxForm(NULL, array(), "field_test_settings_edit");
     $this->assertFieldByName($fieldname, '');
   }