HTTP Response Code
Hyper Text Transfer Protocol or HTTP response status codes are returned when search engines or website visitors make a request to a web server. These codes with three digit value indicate the response and status of HTTP requests. The HTTP response starts form 1xx, 2xx, 3xx, 4xx and 5xx for 1xx I suggest you do some search
Essential HTTP Status Codes for Search Engine and Search Engine Optimization
200 Status Code Ok
The Server has understood the request and returned with a success message.
301 Status Code
An HTTP status code returned by a web server indicating that content has been moved from one location to another. A 301 status code indicates a permanent server redirect, which is a signal that the original page no longer exists and that users and search engines should view the new page as the canonical version of that content.