What is a 404 page exactly?

A 404 page is a page most websites have, or should have, that indicates to the user that the domain they requested, the URL path, is null or provides no information.

A URL stands for Uniform Resource Locator, which is just tech-speak for a web address.
Sometimes, web sites have pages that are broken, or had information at one time but perhaps it has been moved and is no longer available.
A 404 page let's the user know they are at the right site but that the page on the site isn't working.

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