This website extensively uses HTTP status codes to understand how webpages are responding to requests.

HTTP status codes are issued by web servers indicating the status of an http request.

HTTP requests are made when you click on a link or type in the address of a website you would like to visit. (In fact every element, image, file or document that is passed between client and server is controlled by multiple http requests).

When this happens your browser requests the resource (generally a document or image*) from the appropriate location. (How it knows the location is down to DNS but for the time being this is not important).

The location will be a web server of some type, this web server will reply with some standard information (along with the resource requested if it exists).

This standard information allows consistent and predictable performance, and essentially allows the internet to function.

The HTTP Status tells your browser how to act in response, for example, if the status returned is "200" this means that the request was successfully received, understood, and accepted. The resource requested can be displayed as normal.

However a status of "404" means that the resource is unknown or missing, the web server can deal with this in a number of ways (which essentially is what this website is about), but in general this status indicates that an error needs to be displayed.

Status codes are important, if they did not exist, you would spend a long time waiting for resources that may or may not exist. Also, resources that moved would be lost, it is therefore important that the correct codes are used at all times.

* http resources could include anything with a individual identity. The internet is mostly made up of HTML documents and images and so these are the most commonly requested resources, however programs, scripts, animations, xml news feeds are all examples of other types of resource.