diff --git a/core/modules/file/migration_templates/d6_upload.yml b/core/modules/file/migration_templates/d6_upload.yml
index 8289d56..a497099 100644
--- a/core/modules/file/migration_templates/d6_upload.yml
+++ b/core/modules/file/migration_templates/d6_upload.yml
@@ -9,7 +9,7 @@ process:
   vid: vid
   type: type
   upload:
-    plugin: iterator
+    plugin: sub_process
     source: upload
     process:
       target_id:
diff --git a/core/modules/migrate/src/Plugin/migrate/process/Iterator.php b/core/modules/migrate/src/Plugin/migrate/process/Iterator.php
index adfd367..5400e18 100644
--- a/core/modules/migrate/src/Plugin/migrate/process/Iterator.php
+++ b/core/modules/migrate/src/Plugin/migrate/process/Iterator.php
@@ -2,138 +2,20 @@
 
 namespace Drupal\migrate\Plugin\migrate\process;
 
-use Drupal\migrate\ProcessPluginBase;
-use Drupal\migrate\MigrateExecutableInterface;
-use Drupal\migrate\Row;
+@trigger_error('The ' . __NAMESPACE__ . '\Iterator is deprecated in
+Drupal 8.4.x and will be removed before Drupal 9.0.0. Instead, use ' . __NAMESPACE__ . '\SubProcess', E_USER_DEPRECATED);
 
 /**
  * Iterates and processes an associative array.
  *
- * The iterator process plugin allows sub-processing of a list of associative
- * arrays. Often source data will include multiple-value properties as
- * associative arrays. For example, for file uploads on Drupal 6, the upload
- * property contains a list of sub-properties.
+ * @deprecated in Drupal 8.4.x and will be removed in Drupal 9.0.x. Use
+ *   \Drupal\migrate\Plugin\migrate\process\SubProcess instead.
  *
- * Available configuration keys:
- *   - process: the plugin(s) that will process each element of the source.
- *   - key: runs the process pipeline for the defined key.
- *
- * Examples:
- *
- * @code
- * source: Array
- * (
- *   [upload] => Array
- *     (
- *       [0] => Array
- *         (
- *           [fid] => 1
- *           [list] => 0
- *           [description] => "File number 1"
- *         )
- *       [1] => Array
- *         (
- *           [fid] => 2
- *           [list] => 1
- *           [description] => "File number 2"
- *         )
- *     )
- * )
- * ...
- * @endcode
- *
- * The iterator process plugin will take these arrays one at a time and run its
- * own process over each one:
- *
- * @code
- * process:
- *   upload:
- *     plugin: iterator
- *     source: upload
- *     process:
- *       target_id:
- *         plugin: migration_lookup
- *         migration: d6_file
- *         source: fid
- *       display: list
- *       description: description
- * @endcode
- *
- * In this case, each item in the upload array will be processed bye the
- * iterator process plugin. The target_id will be found by looking up the
- * destination value from a previous migration. The display and description
- * fields will simply be mapped.
- *
- * The mapping values passed to iterator are special. Numeric values may not be
- * used.
- *
- * @code
- *   field_relationship:
-       -
-         plugin: migration_lookup
- *       migration:
- *         - migration_page
- *         - migration_blog
- *       source: nid
- *     -
- *       plugin: iterator
- *       process:
- *         target_id: '0'
- * @endcode
- * In the migration above, the value mapped to target_id is intentionally '0'.
- *
- * @see \Drupal\migrate\Plugin\MigrateProcessInterface
+ * @see https://www.drupal.org/node/2880427
  *
  * @MigrateProcessPlugin(
  *   id = "iterator",
  *   handle_multiples = TRUE
  * )
  */
-class Iterator extends ProcessPluginBase {
-
-  /**
-   * Runs a process pipeline on each destination property per list item.
-   */
-  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
-    $return = [];
-    if (!is_null($value)) {
-      foreach ($value as $key => $new_value) {
-        $new_row = new Row($new_value, []);
-        $migrate_executable->processRow($new_row, $this->configuration['process']);
-        $destination = $new_row->getDestination();
-        if (array_key_exists('key', $this->configuration)) {
-          $key = $this->transformKey($key, $migrate_executable, $new_row);
-        }
-        $return[$key] = $destination;
-      }
-    }
-    return $return;
-  }
-
-  /**
-   * Runs the process pipeline for the current key.
-   *
-   * @param string|int $key
-   *   The current key.
-   * @param \Drupal\migrate\MigrateExecutableInterface $migrate_executable
-   *   The migrate executable helper class.
-   * @param \Drupal\migrate\Row $row
-   *   The current row after processing.
-   *
-   * @return mixed
-   *   The transformed key.
-   */
-  protected function transformKey($key, MigrateExecutableInterface $migrate_executable, Row $row) {
-    $process = ['key' => $this->configuration['key']];
-    $migrate_executable->processRow($row, $process, $key);
-    return $row->getDestinationProperty('key');
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function multiple() {
-    return TRUE;
-  }
-
-}
+class Iterator extends SubProcess {}
diff --git a/core/modules/migrate/src/Plugin/migrate/process/SubProcess.php b/core/modules/migrate/src/Plugin/migrate/process/SubProcess.php
index adfd367..01ee026 100644
--- a/core/modules/migrate/src/Plugin/migrate/process/SubProcess.php
+++ b/core/modules/migrate/src/Plugin/migrate/process/SubProcess.php
@@ -7,9 +7,9 @@
 use Drupal\migrate\Row;
 
 /**
- * Iterates and processes an associative array.
+ * Processes a row of data as a sub-process.
  *
- * The iterator process plugin allows sub-processing of a list of associative
+ * The sub_process process plugin allows sub-processing of a list of associative
  * arrays. Often source data will include multiple-value properties as
  * associative arrays. For example, for file uploads on Drupal 6, the upload
  * property contains a list of sub-properties.
@@ -42,13 +42,13 @@
  * ...
  * @endcode
  *
- * The iterator process plugin will take these arrays one at a time and run its
- * own process over each one:
+ * The sub_process process plugin will take these arrays one at a time and run
+ * its own process over each one:
  *
  * @code
  * process:
  *   upload:
- *     plugin: iterator
+ *     plugin: sub_process
  *     source: upload
  *     process:
  *       target_id:
@@ -60,12 +60,12 @@
  * @endcode
  *
  * In this case, each item in the upload array will be processed bye the
- * iterator process plugin. The target_id will be found by looking up the
+ * sub_process process plugin. The target_id will be found by looking up the
  * destination value from a previous migration. The display and description
  * fields will simply be mapped.
  *
- * The mapping values passed to iterator are special. Numeric values may not be
- * used.
+ * The mapping values passed to sub_process are special. Numeric values may not
+ * be used.
  *
  * @code
  *   field_relationship:
@@ -76,7 +76,7 @@
  *         - migration_blog
  *       source: nid
  *     -
- *       plugin: iterator
+ *       plugin: sub_process
  *       process:
  *         target_id: '0'
  * @endcode
@@ -85,11 +85,11 @@
  * @see \Drupal\migrate\Plugin\MigrateProcessInterface
  *
  * @MigrateProcessPlugin(
- *   id = "iterator",
+ *   id = "sub_process",
  *   handle_multiples = TRUE
  * )
  */
-class Iterator extends ProcessPluginBase {
+class SubProcess extends ProcessPluginBase {
 
   /**
    * Runs a process pipeline on each destination property per list item.
diff --git a/core/modules/migrate/tests/src/Unit/process/IteratorTest.php b/core/modules/migrate/tests/src/Unit/process/IteratorTest.php
index 993fb92..46daade 100644
--- a/core/modules/migrate/tests/src/Unit/process/IteratorTest.php
+++ b/core/modules/migrate/tests/src/Unit/process/IteratorTest.php
@@ -31,6 +31,8 @@ class IteratorTest extends MigrateTestCase {
 
   /**
    * Tests the iterator process plugin.
+   *
+   * @group legacy
    */
   public function testIterator() {
     $migration = $this->getMigration();
diff --git a/core/modules/migrate/tests/src/Unit/process/SubProcessTest.php b/core/modules/migrate/tests/src/Unit/process/SubProcessTest.php
index 993fb92..791bded 100644
--- a/core/modules/migrate/tests/src/Unit/process/SubProcessTest.php
+++ b/core/modules/migrate/tests/src/Unit/process/SubProcessTest.php
@@ -4,21 +4,21 @@
 
 use Drupal\migrate\MigrateExecutable;
 use Drupal\migrate\Plugin\migrate\process\Get;
-use Drupal\migrate\Plugin\migrate\process\Iterator;
+use Drupal\migrate\Plugin\migrate\process\SubProcess;
 use Drupal\migrate\Row;
 use Drupal\Tests\migrate\Unit\MigrateTestCase;
 
 /**
- * Tests the iterator process plugin.
+ * Tests the sub_process process plugin.
  *
  * @group migrate
  */
-class IteratorTest extends MigrateTestCase {
+class SubProcessTest extends MigrateTestCase {
 
   /**
-   * The iterator plugin being tested.
+   * The sub_process plugin being tested.
    *
-   * @var \Drupal\migrate\Plugin\migrate\process\TestIterator
+   * @var \Drupal\migrate\Plugin\migrate\process\SubProcess
    */
   protected $plugin;
 
@@ -30,11 +30,11 @@ class IteratorTest extends MigrateTestCase {
   ];
 
   /**
-   * Tests the iterator process plugin.
+   * Tests the sub_process process plugin.
    */
-  public function testIterator() {
+  public function testSubProcess() {
     $migration = $this->getMigration();
-    // Set up the properties for the iterator.
+    // Set up the properties for the sub_process.
     $configuration = [
       'process' => [
         'foo' => 'source_foo',
@@ -42,15 +42,15 @@ public function testIterator() {
       ],
       'key' => '@id',
     ];
-    $plugin = new Iterator($configuration, 'iterator', []);
+    $plugin = new SubProcess($configuration, 'sub_process', []);
     // Manually create the plugins. Migration::getProcessPlugins does this
     // normally but the plugin system is not available.
     foreach ($configuration['process'] as $destination => $source) {
-      $iterator_plugins[$destination][] = new Get(['source' => $source], 'get', []);
+      $sub_process_plugins[$destination][] = new Get(['source' => $source], 'get', []);
     }
     $migration->expects($this->at(1))
       ->method('getProcessPlugins')
-      ->will($this->returnValue($iterator_plugins));
+      ->will($this->returnValue($sub_process_plugins));
     // Set up the key plugins.
     $key_plugin['key'][] = new Get(['source' => '@id'], 'get', []);
     $migration->expects($this->at(2))