A 404 Not Found is an error code that shows up when you try to visit a web page that doesn’t exist on the server. Imagine you typed in an address on your GPS, but it turns out the building doesn’t exist!
The 404 message means the server itself is working fine, but it couldn’t find the specific webpage you requested. This could happen for a few reasons: maybe the webpage was moved or deleted, or you mistyped the address in the first place.