If you have worked with the Field UI in Drupal 7 you will know that you are able to prevent fields from being displayed when viewing entities (e.g. content, users etc). It was fairly simple, you would go to the Manage Display tab of an entity and move the field to the ‘Hidden’ region as shown in the screenshot below.

So you could hide a fields output from being displayed when viewing that entity. But what about when editing that entity? There was no way in the Drupal 7 Field UI to hide a field on a form. You would have to write some form of hook_form_alter() in a custom module and manually force the field to be hidden, like shown in this example.