HTTP Status code

100s- Informational (this is a request that has been received and the process is continuing)

?200s- Success codes so the request was?received and processed successfully.

300s- Redirection codes. This means the request has been received, but more steps are needed to complete that request.

400s - client errors. This means a request was made, but that page is not valid.

500s- Server errors. This means a valid request was made, but the server failed to complete it.

200 - Okay. This tells the browser or the crawler that the request was?successful.

301, moved permanently. This means that the requested resource has been assigned a new permanent location and any future?references to that resource should use one of the returned URLs.

302 - Found. This is the server is currently responding to the request with a page?from a different location, yet the requester continues to use that original location in the future and this is known as a temporary redirect.

503- Service unavailable. This means?the server cannot handle the request because it is currently overloaded or its maintenance or something is happening. The 503 is a temporary outage and it lets the search engine know that it should come back soon because whatever is happening is really a temporary problem. So, if you're going to do site maintenance, always throw up a 503 error because that lets Google know that there is a maintenance period happening as opposed to a 404 which says everything is missing.