Namespaces

I know this is a very basic question and although I''m not a complete newbie I have never read anything explaining namespaces. I have just been looking at some code from another post and the person used: using namespace std I assume std means standard but what does this mean? Any info on namespaces would be muchly appreciated. Thanks for your time "People spend too much time thinking about the past, whatever else it is, its gone"-Mel Gibson, Man Without A Face