If a web page can’t be found then the interwebs puts up an error message, for a lost page that is a 404 error.
Most blogs, including this one, have a dedicated 404 error page that imparts some useful information rather than just going ERROR!
Geeks with a sense of humor, so that’s all three of us, subvert the 404 page to be funny, silly or clever.
If you want to know more about error messages, and it’s fascinating, then look at this link: 404errorpages.com
If you want really cool and creative error pages then you need this link: http://www.hongkiat.com/blog/60-really-cool-and-creative-error-404-pages/
If you want my 404 error page then you want this link: 404.php