What is use of 404 error page in SEO?

[sanuzafar]

How to create 404 page and what is use of 404 page. please give your suggestion.

[petersonangela]

404 not found is error message representative that the client was able to converse with given server but the server could not find what was requested

[alexanderson]

404 errors are pages which has been crawled by the search engine before the page got deleted

[Wilma Mathis]

404 is a error message occur when Google bot attempts to visit a page that doesn’t exist.