HTTP Status Codes give us clues about the result of our operation. They can be categorized under 5 titles:
4xx Client Error
5xx Server Error
Here are some of the most common ones that hundreds of millions of people encounter every day:
In the case of the HTTP status 200 OK, the web server processed the request successfully and transmitted content back to you. Every time you visit a web page this status is encountered by your web browser but it’s just not shown to you.
404 Not Found
This is a problematic one. 404 is an error and it means requested page, file, media or whatever it is can not be found. It might have been moved or maybe address you have is wrong?
500 Internal Server Error
500 means your request was valid however, it can not be processed. It can be a server problem or a restriction, it could be a tiny glitch, a wrong setting, maybe an intentional problem caused by the administrator or even a memory problem from the server.
400 Bad Request
This means your request is not understood by the server. Usually it means your syntax is problematic unless the server has a serious technical problem which is also a possibility.
502 Bad Gateway
Usually occurs due to configuration errors of settings. It can be a caused by your modem, firewall or router.
You can learn more about HTTP Error and Status codes in this Wikipedia page.