“The server has fulfilled a GET request for the resource, and the response is a representation of the result of one or more instance-manipulations applied to the current instance.“ — wikipedia

“The server has fulfilled a GET request for the resource, and the response is a representation of the result of one or more instance- manipulations applied to the current instance. The actual current instance might not be available except by combining this response with other previous or future responses, as appropriate for the specific instance-manipulation(s). If so, the headers of the resulting instance are the result of combining the headers from the status-226 response and the other instances“ — ietf