404 is the Hypertext Transfer Protocol (HTTP) standard response code that indicates the page the visitor is requesting is not found. There are many reasons why the page returns 404, it could be the page has been deleted, the URL has been changed, and many other possibilities. Here's where the custom 404 page comes into play.
404 is one of the commonly used codes. In fact, different codes are used in different situations. For example:
301 Moved permanently
307 Temporary Redirect
400 Bad Request
500 Internal Server Error
502 Bad Gateway
The above are just some of the commonly seen codes. The list is not exhaustive. You can use this tool to check the returned code
Why Create Custom 404 Page
When the page users try to access does not exist, or users type the wrong URL, the default WordPress 404 page will be displayed
That looks good enough to tell users that the page cannot be found, but it can be improved to make it user-friendly. For example, includes the link to the homepage, list down the frequent access pages, sitemap, etc.
Look at how some of the companies handle the 404 pages:
How To Create Custom 404 Page?
You can control how your 404 page looks and create it your own. Follow the steps below:
Step 1: Create Your Own 404 Error Page in the Text Editor
Step 2: Install and Activate 404 Page plugin. Once activation is done, you can access the settings page from the plugin page or Appearance – 404 Error Page
Under the General tab, select the WordPress 404 Page that you have created earlier via the dropdown and click Save Changes.
Congratulations! You have just created and activated a custom WordPress 404 Page.