Page Not Found. This is something just about everyone has seen at one time or another if you’ve spent anytime online at all. In ‘web’ lingo these types of pages are called 404-pages
frank deardurff

Now you are probably thinking why is a “page not found” or a 404 error page a website mistake, and that would be a fair question to be asking, so let me explain what this mistake is, how you can benefit from it and how to correct it.
First we’ve already mentioned “what” it is but let me explain how “people” get there.
404s are usually found either from a broken link on your website somewhere; or someone has tried to type in a url to a specific page on your site and has either mistyped it or the page is no longer there.
It is possible that you will see in your stats that there have been requests for your robot.txt file which is a common file that search engine spiders look for, and if you don’t have one then a 404 page would be triggered.
Now to explain how 404 pages can “help” you.
There is a lot of discussion about what should or shouldn’t be displayed on your 404 page or if you should even display the error page.
My personal opinion is to display the page but have key elements on the page, such as a logo or look and feel of your website, along with a message saying that the page they are looking for was not found but click here to go to the home page of your website.
Another option is if the visitor hits your 404 page, automatically redirect them to the home page of your website. This option works really well, but in discussions I’ve heard people say that the visitor is a little confused as to what just happened.
By utilizing the custom 404 page, you don’t miss out on the opportunity to connect with that visitor. Without any information on that page the visitor would just enter something else into the web address bar and go elsewhere.
The easiest way to remedy this issue is to log in to your control panel (cpanel) and look for the icon that says “Error Pages.” This will list all of them. Be sure to click the 404 and enter your information there. If you are unsure what to put there you can search Google to see some examples.
If you’re uncomfortable doing this you can easily hire a programmer from getafreelancer.com to quickly do this for you. It is a quick project and once you have a template you can copy and paste it into your other sites.