Okay, let's say you want to start a cooking blog (any other baking fans out there?). You decide to tag each recipe page with possible keywords it could be filed under, and then you create another page aggregating all those tags together, which users can navigate to in order to find recipes to try.
You can see from the two images featured here (courtesy of my favorite cooking blog, Smitten Kitchen) that once you click on a tag, you are brought to a page listing all the recipes that fall under that category.
This may seem like a fairly intuitive way to organize your site. However, users with visual or cognitive limitations may find it difficult to navigate a series of lists like this. For this reason, WCAG asks that you provide users with more than one way to navigate to each page on your site.
There are plenty of ways to provide users with multiple navigation options. Users with visual or cognitive limitations may find it easier, for instance, to use a search function to find the page they're looking for.
Thankfully, Deb Perelman, author of Smitten Kitchen, is all over it.
As another example of this practice in action, let's take a look at the website for the Metropolitan Museum of Art. The Met's website contains numerous image galleries, where users can take virtual tours of the museum's exhibits.
From this view, users can toggle back and forth through the exhibit's artifacts by selecting the arrows found on either side of the page. However, if this method proves too cumbersome, users may also select the "Back to Exhibit Objects" button at the top of the page, which will bring them to a single page containing thumbnails of all the artifacts in the exhibit.
This rule does not apply when the page in question is a part of a set process. For example, say you are filling out a bank transfer form online. After filling out the necessary information fields, you are brought to a page confirming that the transfer has been initiated. Since that confirmation can only come as a result of your transfer, it wouldn't make sense for the bank to provide another means of arriving at that page.