When you or another editor moves a page, the old page name doesn’t go away. Instead, it becomes a redirect page (or simply a redirect). That’s good—other pages in Wikipedia are probably linked to the old name, and the redirect means the links on those other pages still work. They take the reader to the page in its new location.
You need to understand how redirects work for two reasons. First, sometimes a page move causes a double redirect, which you need to fix. Second, if you want, you can create redirects that will catch common spelling mistakes and get the reader to the right page.
Note The editor who moves a page should fix any double redirects the move created (Fixing Double Redirects), and bots will normally fix any that remain, within a couple of days (see page 312). But it’s possible that you might find one.
To understand why redirects exist, and how they work, consider this generic situation: Article A has a direct wikilink to article B. Say you move article B, changing the title to C. When you do, Wikipedia places a notice to itself—a redirect—at page B, pointing to the new name of page C. A reader clicks the link on page A. The software goes to page B, which still exists, but is now a redirect. The software sees the redirect and takes the reader to page C, where the desired article is now located, and displays that.
Why didn’t the Wikipedia software, when you renamed page B to page ...