There is no need to ask "What is
X?! Can you explain to me what
X is?!" when there is a
Wikipedia article about
X which is also one of the first results if you just
Google X.
since he is new to bitcoin, he might not be knowing about the fact that there is google and wikipedia
and more over he wanted to start a new thread over here
and for the topic ,a distributed denial-of-service is used to overload the server so that no new connects can be accepted by the server,which means anyone trying to load the page will take forever to reach the destination