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This response code means that the URI of requested resource has been changed temporarily. Further changes in the URI might be made in the future, so the same URI should be used by the client in future requests.
[MDN]Although the HTTP standard specifies "unauthorized", semantically this response means "unauthenticated". That is, the client must authenticate itself to get the requested response.
[MDN]The client does not have access rights to the content; that is, it is unauthorized, so the server is refusing to give the requested resource. Unlike 401 Unauthorized, the client's identity is known to the server.
[MDN]The server cannot find the requested resource. In the browser, this means the URL is not recognized. In an API, this can also mean that the endpoint is valid but the resource itself does not exist. Servers may also send this response instead of 403 Forbidden to hide the existence of a resource from an unauthorized client. This response code is probably the most well known due to its frequent occurrence on the web.
[MDN]The user has sent too many requests in a given amount of time (rate limiting).
[MDN]The server has encountered a situation it does not know how to handle. This error is generic, indicating that the server cannot find a more appropriate 5XX status code to respond with.
[MDN]The server is not ready to handle the request. Common causes are a server that is down for maintenance or that is overloaded. Note that together with this response, a user-friendly page explaining the problem should be sent. This response should be used for temporary conditions and the Retry-After HTTP header should, if possible, contain the estimated time before the recovery of the service. The webmaster must also take care about the caching-related headers that are sent along with this response, as these temporary condition responses should usually not be cached.
[MDN]