404 error is an HTTP response status code which indicates that the requested page could not be found on the server. This error is generally displayed in the internet browser window just like web pages.

In the context of SEO (Search Engine Optimization), a 404 error is an HTTP status code that indicates that the requested webpage could not be found on the server. It typically occurs when a user tries to access a webpage that no longer exists or has been moved without proper redirection.

From an SEO perspective, encountering a 404 error can have negative implications as it disrupts user experience and can lead to lost traffic and potential indexing issues with search engines. To address 404 errors, webmasters typically set up custom 404 error pages to redirect users to relevant content or provide helpful information, ensuring a better user experience and potentially salvaging any lost traffic or search engine rankings. Additionally, implementing proper redirects (such as 301 redirects) for permanently moved or deleted pages can help mitigate the negative impact of 404 errors on SEO.