You may have noticed errors such as 404 Not Found from time to time while browsing the Internet. The number 404 is a status code used to inform your browser, or other programs requesting resources on the web, about some condition related to that resource. There are actually a bunch of these numbers defined. The following is a short list of some of the more common HTML status codes.

200 OK -- Standard response for successful HTTP requests.
202 Accepted -- The request has been accepted for processing, but the processing has not been completed. You may still be declined the resource however if it is disallowed during processing.
301 Moved Permanently -- This and all future requests should be directed to the given URI.
302 Found -- This is the most popular redirect code, also known as "Moved Temporarily".
400 Bad Request -- The request contains bad syntax or cannot be fulfilled.
403 Forbidden -- The request was a legal request, but the server is refusing to respond to it.
404 Not Found -- The requested resource could not be found but may be available again in the future. Subsequent requests by the client or browser are allowed.
500 Internal Server Error