Error Code 451: Indicates That Web Content is Subjected to Censorship
With few exceptions web statuses in the form of codes are intended to identify errors that occur while loading a website. For example, 404 Error status appears when you try to access content that is not found or not exist anymore. But now there is a code that indicates that a lack of content is deliberately caused. If you see error code 451, it means that on the website is used censorship and “legal obstacles” preventing you view Web content.
In theory, this gives you a much better explanation of the error code 403, indicating that the content is “prohibited”. Yet countries that practice censorship can block the 451 code, so there is no direct confirmation of their actions. The message can be most useful in the free internet countries where bans web content is more likely to be the exception, not the rule.