The browser sends request to the server for a specific url. And server responds with a three digit http status code which indicates whether the request is fulfilled or not. Along with status codes other data required by the browser (for html rendering etc) is also received. These status codes are also utilized by search engine crawlers hence they are important especially when you are redeveloping a website (changing paths). So a small mistake can downgrade your seo rankings.
These status codes can be between 100 and 599.
Common status codes which we normally see
404 – Page Not Found
200 – Ok status
202 – Everything ok but process with complete after some time (asynchronously)
500 – Internal Server Error
401 – Unauthorized
403 – Forbidden
301 – Resource has relocated permanently
307 – Page has temporary moved.
Also status codes has range (GROUPS)
100-199 status codes are mostly informational during processing phase.
200-299 is mostly about success
300-399 are mostly to do with redirection
400-499 client (browser) error codes like wrong url, wrong input timeouts etc.
500-599 server error codes like error in programming, unreachable server,