Manual:Page moving

Moving a page causes the page title to change while the page id remains the same. If a redirect is created under the moved page's former page title, it will have a new page id. Pages can be moved using Special:MovePage (SpecialMovepage.php) or  (ApiMove.php). Hooks that pertain to page moves are SpecialMovepageAfterMove (MovePageForm::doSubmit), TitleMoveComplete (Title::moveTo), and AbortMove (Title::isValidMoveOperation).

Moving a page, and then moving it again, can create double redirects.