Crawl Errors
Crawl errors come up when something happens on a web page that inhibits the ability of bots to crawl the website effectively. Most of the time crawl errors refer to broken links. This happens when a link points to a URL that no longer exists. Two negative things happen with broken links. First, you lose the link juice that gets wasted on a non-existent page. Second, the user experience is worse. If someone clicks on a link and come to a broken page, they are very likely to have a negative experience and leave your website. Google wants to send people to websites that will give searchers a good experience, so a lot of crawl errors lead to lower rankings.
There are 2 main ways to fix crawl errors. The best way is to find the pages on your site that link to the non-existent page, then correct the link to point to the right page. If the link to the page comes from other websites, the easiest way to fix these types of crawl errors is with redirects. A redirect will send someone who clicks on a broken link to, instead of the non-existent page, a chosen substitute URL. This URL will get the traffic and the link juice that is sent to the missing page. Setting up redirects is important to both the rankings and the user experience.
You may have come across 404 pages like this:
