A non-indexable page cannot be indexed by search engines. Consequently, the page can’t be found using search engines. If a page is flagged as non-indexable even though you want users to find it using search engines you should check the following:
If you set a URL or its (parent) directory to “disallow” in the robots.txt file, search engines won’t be able to crawl (and index) said URL or directory. If your page isn’t indexable, make sure it’s not blocked through the robots.txt.
You use the canonical tag to tell search engines which page is canonical. This is important to prevent duplicate content issues. In the case of duplicate content the canonical defines which page should be indexed. If the canonical tag on a page points to a different URL you signal Google that your page shouldn’t be indexed as it’s only a duplicate.
A redirect is used when the content of a page is available at a new URL. The most common redirect is the status code 301 (permanent redirect) and 302 (temporary redirect). When an URL answers with the status code 301(or 302 for an extended period of time) search engines know that the URL isn’t relevant anymore. For more information on status codes, please see our Ryte wiki.