diff --git a/core/lib/Drupal/Core/Render/BareHtmlPageRenderer.php b/core/lib/Drupal/Core/Render/BareHtmlPageRenderer.php
index a7164d9..f95d992 100644
--- a/core/lib/Drupal/Core/Render/BareHtmlPageRenderer.php
+++ b/core/lib/Drupal/Core/Render/BareHtmlPageRenderer.php
@@ -52,7 +52,7 @@ public function renderBarePage(array $content, $title, $page_theme_property, arr
       '#type' => 'html',
       '#attributes' => $attributes,
       'page' => [
-        '#type' => 'page',
+        '#type' => 'body',
         '#theme' => $page_theme_property,
         '#title' => $title,
         'content' => $content,
diff --git a/core/lib/Drupal/Core/Render/Element/Page.php b/core/lib/Drupal/Core/Render/Element/Body.php
similarity index 77%
rename from core/lib/Drupal/Core/Render/Element/Page.php
rename to core/lib/Drupal/Core/Render/Element/Body.php
index b73c808d..46c839a 100644
--- a/core/lib/Drupal/Core/Render/Element/Page.php
+++ b/core/lib/Drupal/Core/Render/Element/Body.php
@@ -2,7 +2,7 @@
 
 /**
  * @file
- * Contains \Drupal\Core\Render\Element\Page.
+ * Contains \Drupal\Core\Render\Element\Body.
  */
 
 namespace Drupal\Core\Render\Element;
@@ -12,9 +12,9 @@
  *
  * This represents the "main part" of the HTML page's body; see html.html.twig.
  *
- * @RenderElement("page")
+ * @RenderElement("body")
  */
-class Page extends RenderElement {
+class Body extends RenderElement {
 
   /**
    * {@inheritdoc}
diff --git a/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php b/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php
index 7e06aab..440b2b7 100644
--- a/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php
+++ b/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php
@@ -102,13 +102,13 @@ public function __construct(TitleResolverInterface $title_resolver, PluginManage
   /**
    * {@inheritdoc}
    *
-   * The entire HTML: takes a #type 'page' and wraps it in a #type 'html'.
+   * The entire HTML: takes a #type 'body' and wraps it in a #type 'html'.
    */
   public function renderResponse(array $main_content, Request $request, RouteMatchInterface $route_match) {
     list($page, $title) = $this->prepare($main_content, $request, $route_match);
 
-    if (!isset($page['#type']) || $page['#type'] !== 'page') {
-      throw new \LogicException('Must be #type page');
+    if (!isset($page['#type']) || $page['#type'] !== 'body') {
+      throw new \LogicException('Must be #type body');
     }
 
     $page['#title'] = $title;
@@ -142,7 +142,7 @@ public function renderResponse(array $main_content, Request $request, RouteMatch
   }
 
   /**
-   * Prepares the HTML body: wraps the main content in #type 'page'.
+   * Prepares the HTML body: wraps the main content in #type 'body'.
    *
    * @param array $main_content
    *   The render array representing the main content.
@@ -153,20 +153,20 @@ public function renderResponse(array $main_content, Request $request, RouteMatch
    *
    * @return array
    *   An array with two values:
-   *   0. A #type 'page' render array.
+   *   0. A #type 'body' render array.
    *   1. The page title.
    *
    * @throws \LogicException
    *   If the selected display variant does not implement PageVariantInterface.
    */
   protected function prepare(array $main_content, Request $request, RouteMatchInterface $route_match) {
-    // If the _controller result already is #type => page,
+    // If the _controller result already is #type => body,
     // we have no work to do: The "main content" already is an entire "page"
     // (see html.html.twig).
-    if (isset($main_content['#type']) && $main_content['#type'] === 'page') {
+    if (isset($main_content['#type']) && $main_content['#type'] === 'body') {
       $page = $main_content;
     }
-    // Otherwise, render it as the main content of a #type => page, by selecting
+    // Otherwise, render it as the main content of a #type => body, by selecting
     // page display variant to do that and building that page display variant.
     else {
       // Select the page display variant to be used to render this main content,
@@ -205,10 +205,10 @@ protected function prepare(array $main_content, Request $request, RouteMatchInte
         ->setMainContent($main_content)
         ->setConfiguration($event->getPluginConfiguration());
 
-      // Generate a #type => page render array using the page display variant,
+      // Generate a #type => body render array using the page display variant,
       // the page display will build the content for the various page regions.
       $page = array(
-        '#type' => 'page',
+        '#type' => 'body',
       );
       $page += $page_display->build();
     }
@@ -237,7 +237,7 @@ protected function prepare(array $main_content, Request $request, RouteMatchInte
    * Invokes the page attachment hooks.
    *
    * @param array &$page
-   *   A #type 'page' render array, for which the page attachment hooks will be
+   *   A #type 'body' render array, for which the page attachment hooks will be
    *   invoked and to which the results will be added.
    *
    * @throws \LogicException
diff --git a/core/modules/block/src/Controller/BlockController.php b/core/modules/block/src/Controller/BlockController.php
index 66ecbbd..e7ddb2c 100644
--- a/core/modules/block/src/Controller/BlockController.php
+++ b/core/modules/block/src/Controller/BlockController.php
@@ -51,12 +51,12 @@ public static function create(ContainerInterface $container) {
    *   The name of the theme.
    *
    * @return array
-   *   A #type 'page' render array containing the block region demo.
+   *   A #type 'body' render array containing the block region demo.
    */
   public function demo($theme) {
     $page = [
       '#title' => $this->themeHandler->getName($theme),
-      '#type' => 'page',
+      '#type' => 'body',
       '#attached' => array(
         'drupalSettings' => [
           // The block demonstration page is not marked as an administrative
diff --git a/core/modules/system/src/Controller/BatchController.php b/core/modules/system/src/Controller/BatchController.php
index 9a0e8f0..64f6645 100644
--- a/core/modules/system/src/Controller/BatchController.php
+++ b/core/modules/system/src/Controller/BatchController.php
@@ -67,7 +67,7 @@ public function batchPage(Request $request) {
     }
     elseif (isset($output)) {
       $page = [
-        '#type' => 'page',
+        '#type' => 'body',
         '#show_messages' => FALSE,
         'content' => $output,
       ];
diff --git a/core/modules/system/tests/modules/error_test/src/Controller/ErrorTestController.php b/core/modules/system/tests/modules/error_test/src/Controller/ErrorTestController.php
index 25ef1c5..ea0f796 100644
--- a/core/modules/system/tests/modules/error_test/src/Controller/ErrorTestController.php
+++ b/core/modules/system/tests/modules/error_test/src/Controller/ErrorTestController.php
@@ -88,7 +88,7 @@ public function triggerPDOException() {
    */
   public function triggerRendererException() {
     return [
-      '#type' => 'page',
+      '#type' => 'body',
       '#post_render' => [
         function () {
           throw new \Exception('This is an exception that occurs during rendering');
diff --git a/core/tests/Drupal/Tests/Core/Render/ElementInfoManagerTest.php b/core/tests/Drupal/Tests/Core/Render/ElementInfoManagerTest.php
index b0ca1f7..440584b 100644
--- a/core/tests/Drupal/Tests/Core/Render/ElementInfoManagerTest.php
+++ b/core/tests/Drupal/Tests/Core/Render/ElementInfoManagerTest.php
@@ -122,13 +122,13 @@ public function providerTestGetInfo() {
     $data = array();
     // Provide an element and expect it is returned.
     $data[] = array(
-      'page',
+      'body',
       array(
-        '#type' => 'page',
+        '#type' => 'body',
         '#theme' => 'page',
         '#defaults_loaded' => TRUE,
       ),
-      array('page' => array(
+      array('body' => array(
         '#theme' => 'page',
       )),
     );
@@ -138,24 +138,24 @@ public function providerTestGetInfo() {
       array(
         '#defaults_loaded' => TRUE,
       ),
-      array('page' => array(
+      array('body' => array(
         '#theme' => 'page',
       )),
     );
     // Provide an element and alter it to ensure it is altered.
     $data[] = array(
-      'page',
+      'body',
       array(
-        '#type' => 'page',
+        '#type' => 'body',
         '#theme' => 'page',
         '#number' => 597219,
         '#defaults_loaded' => TRUE,
       ),
-      array('page' => array(
+      array('body' => array(
         '#theme' => 'page',
       )),
       function ($alter_name, array &$info) {
-        $info['page']['#number'] = 597219;
+        $info['body']['#number'] = 597219;
       }
     );
     return $data;
@@ -197,15 +197,15 @@ public function testGetInfoElementPlugin($plugin_class, $expected_info) {
 
     $element_info->expects($this->once())
       ->method('createInstance')
-      ->with('page')
+      ->with('body')
       ->willReturn($plugin);
     $element_info->expects($this->once())
       ->method('getDefinitions')
       ->willReturn(array(
-        'page' => array('class' => 'TestElementPlugin'),
+        'body' => array('class' => 'TestElementPlugin'),
       ));
 
-    $this->assertEquals($expected_info, $element_info->getInfo('page'));
+    $this->assertEquals($expected_info, $element_info->getInfo('body'));
   }
 
   /**
@@ -218,7 +218,7 @@ public function providerTestGetInfoElementPlugin() {
     $data[] = array(
       'Drupal\Core\Render\Element\ElementInterface',
       array(
-        '#type' => 'page',
+        '#type' => 'body',
         '#theme' => 'page',
         '#defaults_loaded' => TRUE,
       ),
@@ -227,7 +227,7 @@ public function providerTestGetInfoElementPlugin() {
     $data[] = array(
       'Drupal\Core\Render\Element\FormElementInterface',
       array(
-        '#type' => 'page',
+        '#type' => 'body',
         '#theme' => 'page',
         '#input' => TRUE,
         '#value_callback' => array('TestElementPlugin', 'valueCallback'),