The entity type annotations start with some basic information about them: ID, label, and things like that. For example, consider the Node entity:

  *   id = "node",
  *   label = @Translation("Content"),
  *   label_singular = @Translation("content item"),
  *   label_plural = @Translation("content items"),
  *   label_count = @PluralTranslation(
  *     singular = "@count content item",
  *     plural = "@count content items"
  *   ),

These are used in various places in the system to properly reference the entity type by machine and human readable names.