When you visit a website, including the wordpress site or not, you see webpages appear the following errors. Based on the errors that you will know websites getting which errors and how to fix it.
404 File Not Found
: pages, files which you accessed, was deleted or because you typed the wrong path
403 Forbidden/Access Denied
: When you type the wrong password to access a folder on the website, you will receive this message, this set is a security measure for the administrator
400 Bad File Request
: Error in syntax type...wrong path or the wrong type of position dots, commas.
408 Request Timeout
: This error notification server has stopped due to meet the information specified time. The cause is due to server processes information slowly, transmission line is congested or required file size is too large.
500 Internal Server Error
: This is a common error often happened by webmasters for that site, they can make wrong command in httacess file cause this error.
501 Not Implemented
: Error unable to perform your request to the site
502 Service Temporarily Overloaded
: Error 502 due to congestion, network switches may be accessed by more people than should cause overcrowding or the entire bandwidth.
503 Service Unavailable
: these errors due to server busy or overloaded or the server is changed or your network is "broken"
Unable to Locate Host
: The website has hosted on a dead server or Internet connection is down or a mistyped address cause of this error.
Connection Refused by Host
: A polite way to tell you that you typed wrong password or you do not have permission to view this page.
Above is common webpage errors, from now, when you enter a site and see one of these errors then you can know why it got the error
Hope it helps!