There are several web status codes you might come across while browsing the web. Some common status codes include errors 503 which means that the service is unavailable. You have the more popular error 404 which means the page cannot be found (due to it being deleted or moved), and you also have error 403 which means forbidden access.
This is usually displayed when a website’s admin has blocked the website or a particular page from the public, or unauthorized users. That being said, it seems that we can look forward to a new web status code in the form of 451. What does this mean? If you were to ever encounter this code, it means that the website has been censored.
Alternatively it could also mean that there could be legal obstacles preventing you from loading the page, like due to a lawsuit for example. So if you were to encounter such a code, you could interpret it meaning that there is something there that someone doesn’t want you to see. Granted it does seem to be similar to error 403, but 403 could mean that you don’t have the proper credentials, as opposed to an entire website or page being blocked due to censorship.
That being said as the folks at Engadget point out, there could be some countries which might take things further by blocking the 451 code itself which kind of ruins the point, but that’s something worth taking note of.