The term Crawl Error is given to describe when a search engine crawler is unable to crawl through a website. These are divided into two categories by Google’s Search Console: Site Errors and URL Errors.
A Site Error will affect an entire website, meaning that a Google bot is unable to crawl through any webpage on the website. If this happens to a website, it’s a sign that the website may lack server connectivity, or that it features a robots.txt file that prevents Google’s crawlers from indexing pages.
Meanwhile, URL Errors affect specific URLs rather than an entire website from its base URL. This is usually a sign that there are issues with specific URLs, such as 404 errors or Not Followed errors. A high number of URL Errors may affect webpage search engine rank, crawl frequency, and crawl depth, and are to be avoided where possible.