Some common status codes are:

1xx (Provisional Response)
A status code that indicates a provisional response and requires the requester to continue the operation.

Code Description
100 (Continue) The requester should continue making the request. The server returns this code to indicate that it has received the first part of the request and is waiting for the remainder.
101 (Switch protocol) The requester has asked the server to switch protocols, and the server has confirmed and is ready to switch.

2xx (Success)
A status code indicating that the request was successfully processed.
Code Description
200 (Success) The server has successfully processed the request. Typically, this means that the server served the requested web page.
201 (Created) The request was successful and the server created a new resource.
202 (Accepted) The server has accepted the request but has not yet processed it.
203 (Unauthorized Information) The server successfully processed the request, but the information returned may have come from another source.
204 (No Content) The server successfully processed the request but did not return any content.
205 (Reset Content) The server successfully processed the request but did not return any content.
206 (Partial content) The server successfully processed part of the GET request.

3xx (redirect)
indicates that further action is required to complete the request. Typically, these status codes are used for redirects.

Code Description
300 (Multiple choices) In response to requests, the server can perform a variety of operations. The server can select an action based on the requester (user agent) or provide a list of actions for the requester to choose from.
301 (Permanently Moved) The requested web page has been permanently moved to a new location. When the server returns this response (in response to a GET or HEAD request), it automatically forwards the requester to the new location.
302 (Temporary Move) The server is currently responding to requests from a web page in a different location, but the requester should continue to use the original location for future requests.
303 (View Other Locations) The server returns this code when the requester should use separate GET requests to different locations to retrieve the response.
304 (Unmodified) The requested web page has not been modified since the last request. When the server returns this response, no web page content is returned.
305 (Use Proxy) The requester can only use a proxy to access the requested web page. If the server returns this response, it also indicates that the requester should use a proxy.
307 (Temporary Redirect) The server is currently responding to the request from a web page in a different location, but the requester should continue to use the original location for future requests.

4xx (Request Error)
These status codes indicate that the request may have gone wrong, preventing the server from processing it.

Code Description
400 (Bad Request) The server does not understand the syntax of the request.
401 (Unauthorized) The request requires authentication. For web pages that require login, the server may return this response.
403 (Forbidden) The server refused the request.
404 (Not Found) The server cannot find the requested web page.
405 (Method Disabled) Disables the method specified in the request.
406 (Not Acceptable) The requested web page cannot be responded to using the requested content properties.
407 (Proxy Authorization Required) This status code is similar to 401 (Not Authorized), but specifies that the requester should be authorized to use the proxy.
408 (Request Timeout) A timeout occurred while the server was waiting for a request.
409 (Conflict) The server encountered a conflict while completing the request. The server MUST include information about the conflict in the response.
410 (Deleted) The server returns this response if the requested resource has been permanently deleted.
411 (Valid length required) The server does not accept requests without a valid content-length header field.
412 (Precondition not met) The server did not meet one of the preconditions set by the requester in the request.
413 (Request entity too large) The server cannot process the request because the request entity is too large and exceeds the server's processing capabilities.
414 (Requested URI too long) The requested URI (usually a URL) is too long and cannot be processed by the server.
415 (Unsupported Media Type) The requested format is not supported by the requested page.
416 (Requested range does not meet requirements) The server returns this status code if the page cannot provide the requested range.
417 (Expectation Not Met) The server did not meet the requirements for the "expected" request header field.

5xx (Server Error)
These status codes indicate that an internal error occurred while the server was trying to process the request. These errors may be errors on the server itself rather than an error in the request.

Code Description
500 (Server Internal Error) The server encountered an error and was unable to complete the request.
501 (not yet implemented) The server does not have the functionality to complete the request. For example, this code may be returned when the server does not recognize the request method.
502 (Bad Gateway) The server, acting as a gateway or proxy, received an invalid response from the upstream server.
503 (Service Unavailable) The server is currently unavailable (due to overload or downtime for maintenance). Often, this is a temporary state.
504 (Gateway Timeout) The server acts as a gateway or proxy, but does not receive the request from the upstream server in time.
505 (HTTP version not supported) The server does not support the HTTP protocol version used in the request.