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 to do some search hear I am explaining you the rest of the http status codes.
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.