From http://www.w3schools.com (Copyright Refsnes Data)

HTTP Status Messages

When a browser requests a service from a web server, an error might occur.

This is a list of HTTP status messages that might be returned:

1xx: Information

Message:	Description:
100 Continue	Only a part of the request has been received by the server, but as long as it has not been rejected, the client should continue with the request
101 Switching Protocols	The server switches protocol

2xx: Successful

Message:	Description:
200 OK	The request is OK
201 Created	The request is complete, and a new resource is created
202 Accepted	The request is accepted for processing, but the processing is not complete
203 Non-authoritative Information
204 No Content
205 Reset Content
206 Partial Content

3xx: Redirection

Message:	Description:
300 Multiple Choices	A link list. The user can select a link and go to that location. Maximum five addresses
301 Moved Permanently	The requested page has moved to a new url
302 Found	The requested page has moved temporarily to a new url
303 See Other	The requested page can be found under a different url
304 Not Modified
305 Use Proxy
306 Unused	This code was used in a previous version. It is no longer used, but the code is reserved
307 Temporary Redirect	The requested page has moved temporarily to a new url

4xx: Client Error

Message:	Description:
400 Bad Request	The server did not understand the request
401 Unauthorized	The requested page needs a username and a password
402 Payment Required	You can not use this code yet
403 Forbidden	Access is forbidden to the requested page
404 Not Found	The server can not find the requested page
405 Method Not Allowed	The method specified in the request is not allowed
406 Not Acceptable	The server can only generate a response that is not accepted by the client
407 Proxy Authentication Required	You must authenticate with a proxy server before this request can be served
408 Request Timeout	The request took longer than the server was prepared to wait
409 Conflict	The request could not be completed because of a conflict
410 Gone	The requested page is no longer available
411 Length Required	The "Content-Length" is not defined. The server will not accept the request without it
412 Precondition Failed	The precondition given in the request evaluated to false by the server
413 Request Entity Too Large	The server will not accept the request, because the request entity is too large
414 Request-url Too Long	The server will not accept the request, because the url is too long. Occurs when you convert a "post" request to a "get" request with a long query information
415 Unsupported Media Type	The server will not accept the request, because the media type is not supported
416
417 Expectation Failed

5xx: Server Error

Message:	Description:
500 Internal Server Error	The request was not completed. The server met an unexpected condition
501 Not Implemented	The request was not completed. The server did not support the functionality required
502 Bad Gateway	The request was not completed. The server received an invalid response from the upstream server
503 Service Unavailable	The request was not completed. The server is temporarily overloading or down
504 Gateway Timeout	The gateway has timed out
505 HTTP Version Not Supported	The server does not support the "http protocol" version