A HTTP status code is a three-digit number that states how a request for a given webpage or file was handled. A code may signify that the request worked (e.g. 200) or that it was missing (404) or there was an error (500).
There are a huge number of HTTP status codes, but the first digit of each will tell you whether it was successful or not:
2xx– any code beginning with 2 was successful in some way. The most common response is 200, meaning everything was OK.3xx– any code beginning with 3 was redirected somewhere else. Common examples include 301 (Moved Permanently) and 302 (Moved Temporarily).4xx– any code beginning with 4 signifies an error in the request itself, called a “client error”. Common examples include 404 (Not Found) and 403 (Forbidden).5xx–any code beginning with 5 signifies that an error occurred processing the request, called a “server error”. The most common example is 500, meaning that an unspecified error occurred.
Further reading
List of HTTP status codes – Wikipedia