gistfile1.php

<?php
    // My code for getting this output.
    $definition = new DataDefinition(\Drupal::service('typed_data')->getDefinition('entity'));
    $definition->setDataType('entity');
    $definition->addConstraint('EntityType', 'node');
    drupal_set_message('<pre>' . print_r($definition, TRUE) . '</pre>');
    $definition2 = new DataDefinition(\Drupal::service('typed_data')->getDefinition('entity:node'));
    drupal_set_message('<pre>' . print_r($definition2, TRUE) . '</pre>');

gistfile2.txt

// $definition print_r()

Drupal\Core\TypedData\DataDefinition Object
(
    [definition:protected] => Array
        (
            [list_class] => \Drupal\Core\TypedData\Plugin\DataType\ItemList
            [id] => entity
            [label] => Entity
            [description] => All kind of entities, e.g. nodes, comments or users.
            [derivative] => \Drupal\Core\Entity\Plugin\DataType\Deriver\EntityDeriver
            [class] => Drupal\Core\Entity\Plugin\DataType\Entity
            [provider] => Core
            [type] => entity
            [constraints] => Array
                (
                    [EntityType] => node
                )

        )

)

gistfile3.txt

// $definition2 print_r()

Drupal\Core\TypedData\DataDefinition Object
(
    [definition:protected] => Array
        (
            [label] => Content
            [class] => Drupal\node\Entity\Node
            [constraints] => Array
                (
                    [EntityType] => node
                )

            [list_class] => \Drupal\Core\TypedData\Plugin\DataType\ItemList
            [id] => entity
            [description] => All kind of entities, e.g. nodes, comments or users.
            [derivative] => \Drupal\Core\Entity\Plugin\DataType\Deriver\EntityDeriver
            [provider] => Core
        )

)