There are lots of jokes about HTTP status codes, what they mean, and general frustration with the inconsistent way in which they're used.
- 100: Continue sending me the request.
- 200: OK, here you go.
- 201: OK, I created it for you.
- 301: Moved what you want to a new spot over here.
- 302: Found what you're looking for over here.
- 400: Your bad.
- 401: You aren't logged in.
- 403: You're logged in, but can't do/see that.
HTTP 5xx: Our bad
- 500: We screwed up.
- 503: We forgot to start the server.
There are many more status codes, and as a developer I ecourage other developers to use appropriate and specific response codes. For more specific details, Wikipedia has a good overview.