The server is refusing to service the request because the request-target is longer than the server is willing to interpret.
This rare condition is only likely to occur when a client has improperly converted a POST request to a GET request with long query information, when the client has descended into a redirect “black hole” (e.g., a redirected URI prefix that points to a suffix of itself), or when the server is under attack by a client attempting to exploit potential security holes.
A 414 response is cacheable by default; that is, unless otherwise indicated by the method definition or explicit cache controls.